Fix pg_dump dependency on postgres.h

Attached patch removes pg_dump dependency on postgres.h. The main reason
for that was discussed there:

http://archives.postgresql.org/pgsql-hackers/2007-10/msg01261.php

This fix contains several steps:

1) I removed sugar word from postgres.h and put them closer to consumer
:-). I created include/catalog/genbki.h which contains sugar words -
macros for correct catalog data processing. All catalogs file now
include this header.

2) I moved SEQ_MAXVALUE and SEQ_MINVALUE macros from sequence.h to
postgres_config_manual.h


3) I created two new headers pg_type_fn.h and pg_proc_fn.h and I moved
all extern function definition from related headers into them. Second
possible solution could be let function definition into headers and
fence them by #ifndef FRONTED.

    Let me know your comments.

        Thanks
            Zdenek