pgsql: Add PG_VERSION_NUM for use by 3rd party applications wanting to

Log Message:
-----------
Add PG_VERSION_NUM for use by 3rd party applications wanting to test the
backend version in C using > and < comparisons.

Modified Files:
--------------
pgsql:
configure (r1.480 -> r1.481)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.diff?r1=1.480&amp;r2=1.481)
configure.in (r1.450 -> r1.451)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.in.diff?r1=1.450&amp;r2=1.451)
pgsql/src/include:
pg_config.h.in (r1.93 -> r1.94)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config.h.in.diff?r1=1.93&amp;r2=1.94)