Patch to include c.h

I noticed that xlog.h uses PGDLLIMPORT, but it does not include c.h
directly or indirectly. Also, in timestamp.h different code is enabled
depending on HAVE_INT64_TMESTAMP being defined, but even though that macro
is defined in pg_config.h, it does not automatically trickle down into this
file, as it is supposed to.

Apparently all .c files manage to include c.h (directly or indirectly)
before including these files, so the compilers do the right thing. But I
caught these since I tried using an IDE, and it grays out sections to, or
shows error-markers when it doesn't find a macro included directly or
indirectly.

I vaguely remember a discussion where (I think) Bruce mentioned that we do
or intend to do some kind of compilability check on individual h files. DO
we have something in place to catch such things? I am sure there are many
other places where such inclusions are omitted, but these are the ones I
found on my first attempts to use this IDE.

Best regards,
--
Gurjeet Singh

http://gurjeet.singh.im/