Pin the built-in index access methods.

This was overlooked in commit 473b9328, which introduced DROP ACCESS
METHOD.  Although that command is restricted to superusers, we don't want
even superusers dropping the built-in methods; "DROP ACCESS METHOD btree"
in particular is unrecoverable from.  Pin these objects in the same way
that other initdb-created objects are pinned.

I chose to bump catversion for this fix.  That's not absolutely necessary
perhaps, but it will ensure that no 9.6 production systems are missing
the pin entries.

src/bin/initdb/initdb.c

@@ -1664,6 +1664,8 @@ setup_depend(FILE *cmdfd)
 		"INSERT INTO pg_depend SELECT 0,0,0, tableoid,oid,0, 'p' "
 		" FROM pg_opfamily;\n\n",
 		"INSERT INTO pg_depend SELECT 0,0,0, tableoid,oid,0, 'p' "
+		" FROM pg_am;\n\n",
+		"INSERT INTO pg_depend SELECT 0,0,0, tableoid,oid,0, 'p' "
 		" FROM pg_amop;\n\n",
 		"INSERT INTO pg_depend SELECT 0,0,0, tableoid,oid,0, 'p' "
 		" FROM pg_amproc;\n\n",

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201605051
+#define CATALOG_VERSION_NO	201605191
 
 #endif