Invalid reference to ForkNumber enum

Hello,

There is an invalid reference to ForkNumber definition (from commit
f71939cd).
It was defined in relfilenode.h at time of the commit
(https://github.com/postgres/postgres/blob/f71939cd/src/include/storage/relfilenode.h),
but now it's defined in relpath.h
(https://github.com/postgres/postgres/blob/master/src/include/common/relpath.h).
Patch attached.

Best regards,
Alexander