Split out rmgr rm_desc functions into their own files

This is necessary (but not sufficient) to have them compilable outside
of a backend environment.

src/backend/access/rmgrdesc/dbasedesc.c

@@ -0,0 +1,43 @@
+/*-------------------------------------------------------------------------
+ *
+ * dbasedesc.c
+ *    rmgr descriptor routines for commands/dbcommands.c
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *    src/backend/access/rmgrdesc/dbasedesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "commands/dbcommands.h"
+#include "lib/stringinfo.h"
+
+
+void
+dbase_desc(StringInfo buf, uint8 xl_info, char *rec)
+{
+	uint8		info = xl_info & ~XLR_INFO_MASK;
+
+	if (info == XLOG_DBASE_CREATE)
+	{
+		xl_dbase_create_rec *xlrec = (xl_dbase_create_rec *) rec;
+
+		appendStringInfo(buf, "create db: copy dir %u/%u to %u/%u",
+						 xlrec->src_db_id, xlrec->src_tablespace_id,
+						 xlrec->db_id, xlrec->tablespace_id);
+	}
+	else if (info == XLOG_DBASE_DROP)
+	{
+		xl_dbase_drop_rec *xlrec = (xl_dbase_drop_rec *) rec;
+
+		appendStringInfo(buf, "drop db: dir %u/%u",
+						 xlrec->db_id, xlrec->tablespace_id);
+	}
+	else
+		appendStringInfo(buf, "UNKNOWN");
+}