Fix a passel of recently-committed violations of the rule 'thou shalt

have no other gods before c.h'.  Also remove some demonstrably redundant
#include lines, mostly of <errno.h> which was added to c.h years ago.

contrib/btree_gist/btree_numeric.c

@@ -1,7 +1,8 @@
+#include "btree_gist.h"
+
 #include <math.h>
 #include <float.h>
 
-#include "btree_gist.h"
 #include "btree_utils_var.h"
 #include "utils/builtins.h"
 #include "utils/numeric.h"

contrib/btree_gist/btree_utils_num.h

@@ -1,11 +1,11 @@
 #ifndef __BTREE_UTILS_NUM_H__
 #define __BTREE_UTILS_NUM_H__
 
+#include "btree_gist.h"
+
 #include <math.h>
 #include <float.h>
 
-#include "btree_gist.h"
-
 typedef char GBT_NUMKEY;
 
 /* Better readable key */

contrib/btree_gist/btree_utils_var.c

@@ -1,8 +1,9 @@
+#include "btree_gist.h"
+
 #include <math.h>
 #include <limits.h>
 #include <float.h>
 
-#include "btree_gist.h"
 #include "btree_utils_var.h"
 #include "utils/pg_locale.h"
 #include "utils/builtins.h"

contrib/btree_gist/btree_utils_var.h

@@ -1,10 +1,10 @@
 #ifndef __BTREE_UTILS_VAR_H__
 #define __BTREE_UTILS_VAR_H__
 
-#include "mb/pg_wchar.h"
-
 #include "btree_gist.h"
 
+#include "mb/pg_wchar.h"
+
 /* Variable length key */
 typedef bytea GBT_VARKEY;