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/tblspcdesc.c

@@ -0,0 +1,40 @@
+/*-------------------------------------------------------------------------
+ *
+ * tblspcdesc.c
+ *    rmgr descriptor routines for commands/tablespace.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/tblspcdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "commands/tablespace.h"
+
+
+void
+tblspc_desc(StringInfo buf, uint8 xl_info, char *rec)
+{
+	uint8		info = xl_info & ~XLR_INFO_MASK;
+
+	if (info == XLOG_TBLSPC_CREATE)
+	{
+		xl_tblspc_create_rec *xlrec = (xl_tblspc_create_rec *) rec;
+
+		appendStringInfo(buf, "create tablespace: %u \"%s\"",
+						 xlrec->ts_id, xlrec->ts_path);
+	}
+	else if (info == XLOG_TBLSPC_DROP)
+	{
+		xl_tblspc_drop_rec *xlrec = (xl_tblspc_drop_rec *) rec;
+
+		appendStringInfo(buf, "drop tablespace: %u", xlrec->ts_id);
+	}
+	else
+		appendStringInfo(buf, "UNKNOWN");
+}