pgsql: Put back storage/proc.h in postmaster.c.

Put back storage/proc.h in postmaster.c.

I took this out thinking it wasn't needed anymore, but the EXEC_BACKEND
code still needs it.  Per buildfarm.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/57b9bdda39e05d127f6930045d289ffc9935c971

Modified Files
--------------
src/backend/postmaster/postmaster.c |    1 +
1 files changed, 1 insertions(+), 0 deletions(-)