pg_filedump 9.3: checksums (and a few other fixes)

Attached is a first draft of an update to pg_filedump for 9.3. I know
pg_filedump is a pgfoundry project, but that seems like it's just there
to host the download; so please excuse the slightly off-topic post here
on -hackers.

I made a few changes to support 9.3, which were mostly fixes related two
things:

 * new htup_details.h and changes related to FK concurrency improvements
 * XLogRecPtr is now a uint64

And, of course, I added support for checksums. They are always displayed
and calculated, but it only throws an error if you pass "-k". Only the
user knows whether checksums are enabled, because we removed page-level
bits indicating the presence of a checksum.

The patch is a bit ugly: I had to copy some code, and copy the entire
checksum.c file (minus some Asserts, which don't work in an external
program). Suggestions welcome.

Regards,
    Jeff Davis