pgsql: Move RelFileNumber declarations to common/relpath.h.

Move RelFileNumber declarations to common/relpath.h.

Previously, these were declared in postgres_ext.h, but they are not
needed nearly so widely as the OID declarations, so that doesn't
necessarily make sense. Also, because postgres_ext.h is included
before most of c.h has been processed, the previous location creates
some problems for a pending patch.

Patch by me, reviewed by Dilip Kumar.

Discussion: http://postgr.es/m/CA+TgmoYc8oevMqRokZQ4y_6aRn-7XQny1JBr5DyWR_jiFtONHw@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/2f47715cc8649f854b1df28dfc338af9801db217

Modified Files
--------------
src/bin/pg_dump/pg_dump.c | 1 +
src/bin/pg_upgrade/pg_upgrade.h | 1 +
src/include/catalog/binary_upgrade.h | 2 ++
src/include/common/relpath.h | 7 +++++++
src/include/nodes/parsenodes.h | 1 +
src/include/nodes/plannodes.h | 1 +
src/include/postgres_ext.h | 8 --------
src/include/utils/relcache.h | 1 +
8 files changed, 14 insertions(+), 8 deletions(-)