Adjust many backend functions to return OID rather than void.

Extracted from a larger patch by Dimitri Fontaine.  It is hoped that
this will provide infrastructure for enriching the new event trigger
functionality, but it seems possibly useful for other purposes as
well.

src/backend/commands/tablespace.c

@@ -818,9 +818,10 @@ directory_is_empty(const char *path)
 /*
  * Rename a tablespace
  */
-void
+Oid
 RenameTableSpace(const char *oldname, const char *newname)
 {
+	Oid			tspId;
 	Relation	rel;
 	ScanKeyData entry[1];
 	HeapScanDesc scan;
@@ -843,6 +844,7 @@ RenameTableSpace(const char *oldname, const char *newname)
 				 errmsg("tablespace \"%s\" does not exist",
 						oldname)));
 
+	tspId = HeapTupleGetOid(tup);
 	newtuple = heap_copytuple(tup);
 	newform = (Form_pg_tablespace) GETSTRUCT(newtuple);
 
@@ -881,6 +883,8 @@ RenameTableSpace(const char *oldname, const char *newname)
 	CatalogUpdateIndexes(rel, newtuple);
 
 	heap_close(rel, NoLock);
+
+	return tspId;
 }
 
 /*