Commit the reasonably uncontroversial parts of J.R. Nield's PITR patch, to

wit: Add a header record to each WAL segment file so that it can be reliably
identified.  Avoid splitting WAL records across segment files (this is not
strictly necessary, but makes it simpler to incorporate the header records).
Make WAL entries for file creation, deletion, and truncation (as foreseen but
never implemented by Vadim).  Also, add support for making XLOG_SEG_SIZE
configurable at compile time, similarly to BLCKSZ.  Fix a couple bugs I
introduced in WAL replay during recent smgr API changes.  initdb is forced
due to changes in pg_control contents.

src/include/pg_config_manual.h

@@ -6,7 +6,7 @@
  * for developers.	If you edit any of these, be sure to do a *full*
  * rebuild (and an initdb if noted).
  *
- * $PostgreSQL: pgsql/src/include/pg_config_manual.h,v 1.9 2004/01/06 17:26:23 neilc Exp $
+ * $PostgreSQL: pgsql/src/include/pg_config_manual.h,v 1.10 2004/02/11 22:55:26 tgl Exp $
  *------------------------------------------------------------------------
  */
 
@@ -43,6 +43,14 @@
  */
 #define RELSEG_SIZE (0x40000000 / BLCKSZ)
 
+/*
+ * XLOG_SEG_SIZE is the size of a single WAL file.  This must be a power of 2
+ * and larger than BLCKSZ (preferably, a great deal larger than BLCKSZ).
+ *
+ * Changing XLOG_SEG_SIZE requires an initdb.
+ */
+#define XLOG_SEG_SIZE	(16*1024*1024)
+
 /*
  * Maximum number of columns in an index and maximum number of
  * arguments to a function. They must be the same value.