Move Timestamp/Interval typedefs and basic macros into datatype/timestamp.h.

As per my recent proposal, this refactors things so that these typedefs and
macros are available in a header that can be included in frontend-ish code.
I also changed various headers that were undesirably including
utils/timestamp.h to include datatype/timestamp.h instead.  Unsurprisingly,
this showed that half the system was getting utils/timestamp.h by way of
xlog.h.

No actual code changes here, just header refactoring.

src/backend/access/transam/twophase.c

@@ -64,6 +64,7 @@
 #include "storage/smgr.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
+#include "utils/timestamp.h"
 
 
 /*

src/backend/access/transam/xact.c

@@ -49,6 +49,7 @@
 #include "utils/memutils.h"
 #include "utils/relmapper.h"
 #include "utils/snapmgr.h"
+#include "utils/timestamp.h"
 #include "pg_trace.h"
 
 

src/backend/access/transam/xlog.c

@@ -58,6 +58,7 @@
 #include "utils/guc.h"
 #include "utils/ps_status.h"
 #include "utils/relmapper.h"
+#include "utils/timestamp.h"
 #include "pg_trace.h"
 
 

src/backend/commands/analyze.c

@@ -48,6 +48,7 @@
 #include "utils/pg_rusage.h"
 #include "utils/syscache.h"
 #include "utils/tuplesort.h"
+#include "utils/timestamp.h"
 #include "utils/tqual.h"
 
 

src/backend/commands/async.c

@@ -132,6 +132,7 @@
 #include "utils/builtins.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
+#include "utils/timestamp.h"
 
 
 /*

src/backend/commands/prepare.c

@@ -31,6 +31,7 @@
 #include "tcop/utility.h"
 #include "utils/builtins.h"
 #include "utils/snapmgr.h"
+#include "utils/timestamp.h"
 
 
 /*

src/backend/commands/user.c

@@ -33,6 +33,7 @@
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/syscache.h"
+#include "utils/timestamp.h"
 #include "utils/tqual.h"
 
 /* Potentially set by contrib/pg_upgrade_support functions */

src/backend/commands/vacuumlazy.c

@@ -53,6 +53,7 @@
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/pg_rusage.h"
+#include "utils/timestamp.h"
 #include "utils/tqual.h"
 
 

src/backend/commands/variable.c

@@ -26,6 +26,7 @@
 #include "utils/builtins.h"
 #include "utils/syscache.h"
 #include "utils/snapmgr.h"
+#include "utils/timestamp.h"
 #include "mb/pg_wchar.h"
 
 /*

src/backend/libpq/crypt.c

@@ -26,6 +26,7 @@
 #include "miscadmin.h"
 #include "utils/builtins.h"
 #include "utils/syscache.h"
+#include "utils/timestamp.h"
 
 
 int

src/backend/parser/parse_node.c

@@ -24,6 +24,7 @@
 #include "parser/parse_expr.h"
 #include "parser/parse_relation.h"
 #include "utils/builtins.h"
+#include "utils/int8.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 #include "utils/varbit.h"

src/backend/postmaster/autovacuum.c

@@ -97,6 +97,7 @@
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
 #include "utils/syscache.h"
+#include "utils/timestamp.h"
 #include "utils/tqual.h"
 
 

src/backend/postmaster/pgstat.c

@@ -62,6 +62,7 @@
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/rel.h"
+#include "utils/timestamp.h"
 #include "utils/tqual.h"
 
 

src/backend/replication/walreceiver.c

@@ -50,6 +50,7 @@
 #include "utils/guc.h"
 #include "utils/ps_status.h"
 #include "utils/resowner.h"
+#include "utils/timestamp.h"
 
 /* Global variable to indicate if this process is a walreceiver process */
 bool		am_walreceiver;

src/backend/replication/walsender.c

@@ -62,6 +62,7 @@
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/resowner.h"
+#include "utils/timestamp.h"
 
 
 /* Array of WalSnds in shared memory */

src/backend/storage/buffer/bufmgr.c

@@ -47,6 +47,7 @@
 #include "storage/standby.h"
 #include "utils/rel.h"
 #include "utils/resowner.h"
+#include "utils/timestamp.h"
 
 
 /* Note: these two macros only work on shared buffers, not local ones! */

src/backend/storage/ipc/standby.c

@@ -28,6 +28,7 @@
 #include "storage/sinvaladt.h"
 #include "storage/standby.h"
 #include "utils/ps_status.h"
+#include "utils/timestamp.h"
 
 /* User-settable GUC parameters */
 int			vacuum_defer_cleanup_age;

src/backend/storage/lmgr/proc.c

@@ -47,6 +47,7 @@
 #include "storage/procarray.h"
 #include "storage/procsignal.h"
 #include "storage/spin.h"
+#include "utils/timestamp.h"
 
 
 /* GUC variables */

src/backend/tcop/postgres.c

@@ -72,6 +72,7 @@
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/snapmgr.h"
+#include "utils/timestamp.h"
 #include "mb/pg_wchar.h"
 
 

src/backend/utils/adt/date.c

@@ -27,6 +27,7 @@
 #include "utils/array.h"
 #include "utils/builtins.h"
 #include "utils/date.h"
+#include "utils/datetime.h"
 #include "utils/nabstime.h"
 
 /*

src/backend/utils/adt/genfile.c

@@ -28,6 +28,7 @@
 #include "storage/fd.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
+#include "utils/timestamp.h"
 
 typedef struct
 {

src/backend/utils/adt/misc.c

@@ -20,8 +20,8 @@
 #include <math.h>
 
 #include "catalog/catalog.h"
-#include "catalog/pg_type.h"
 #include "catalog/pg_tablespace.h"
+#include "catalog/pg_type.h"
 #include "commands/dbcommands.h"
 #include "funcapi.h"
 #include "miscadmin.h"
@@ -30,8 +30,9 @@
 #include "storage/fd.h"
 #include "storage/pmsignal.h"
 #include "storage/procarray.h"
-#include "utils/builtins.h"
 #include "tcop/tcopprot.h"
+#include "utils/builtins.h"
+#include "utils/timestamp.h"
 
 #define atooid(x)  ((Oid) strtoul((x), NULL, 10))
 

src/backend/utils/adt/nabstime.c

@@ -25,6 +25,7 @@
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
 #include "utils/builtins.h"
+#include "utils/datetime.h"
 #include "utils/nabstime.h"
 
 #define MIN_DAYNUM (-24856)		/* December 13, 1901 */

src/backend/utils/adt/pgstatfuncs.c

@@ -14,13 +14,14 @@
  */
 #include "postgres.h"
 
+#include "catalog/pg_type.h"
 #include "funcapi.h"
+#include "libpq/ip.h"
 #include "miscadmin.h"
 #include "pgstat.h"
-#include "catalog/pg_type.h"
 #include "utils/builtins.h"
 #include "utils/inet.h"
-#include "libpq/ip.h"
+#include "utils/timestamp.h"
 
 /* bogus ... these externs should be in a header file */
 extern Datum pg_stat_get_numscans(PG_FUNCTION_ARGS);

src/backend/utils/adt/selfuncs.c

@@ -124,6 +124,7 @@
 #include "utils/selfuncs.h"
 #include "utils/spccache.h"
 #include "utils/syscache.h"
+#include "utils/timestamp.h"
 #include "utils/tqual.h"
 
 

src/backend/utils/mmgr/portalmem.c

@@ -24,6 +24,7 @@
 #include "miscadmin.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
+#include "utils/timestamp.h"
 
 /*
  * Estimate of the maximum number of open portals a user would have,