Split hash.h → hash_xlog.h

Since the hash AM is going to be revamped to have WAL, this is a good
opportunity to clean up the include file a little bit to avoid including
a lot of extra stuff in the future.

Author: Amit Kapila

src/backend/access/hash/hash.c

@@ -19,6 +19,7 @@
 #include "postgres.h"
 
 #include "access/hash.h"
+#include "access/hash_xlog.h"
 #include "access/relscan.h"
 #include "catalog/index.h"
 #include "commands/vacuum.h"