pgsql: Fix problems with PGXS builds against an installation tree that

Log Message:
-----------
Fix problems with PGXS builds against an installation tree that was
relocated after installation. We can't trust the installation paths
inserted into Makefile.global by configure, so instead we must get the
paths from pg_config. This requires extending pg_config to support all
the separately-configurable path names, but that was on TODO anyway.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
pg_config-ref.sgml (r1.21 -> r1.22)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_config-ref.sgml.diff?r1=1.21&r2=1.22)
pgsql/src:
Makefile.global.in (r1.219 -> r1.220)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/Makefile.global.in.diff?r1=1.219&r2=1.220)
pgsql/src/bin/pg_config:
pg_config.c (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_config/pg_config.c.diff?r1=1.12&r2=1.13)
win32.mak (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_config/win32.mak.diff?r1=1.2&r2=1.3)
pgsql/src/bin/psql:
bcc32.mak (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/bcc32.mak.diff?r1=1.14&r2=1.15)
win32.mak (r1.28 -> r1.29)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/win32.mak.diff?r1=1.28&r2=1.29)
pgsql/src/include:
port.h (r1.82 -> r1.83)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/port.h.diff?r1=1.82&r2=1.83)
pgsql/src/port:
Makefile (r1.28 -> r1.29)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/Makefile.diff?r1=1.28&r2=1.29)
path.c (r1.58 -> r1.59)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/path.c.diff?r1=1.58&r2=1.59)