Bump PG_CONTROL_VERSION for previous 9.4 changes.

This should have been done in 6bc8ef0b7f1f1df3998745a66e1790e27424aa0c
and/or 50e547096c4858a68abf09894667a542cc418315, but better late than
never.  If we don't change this then we risk 9.3 pg_controldata or
pg_resetxlog being inappropriately used against a 9.4 pg_control file,
or vice versa.