pgsql: Make numeric form of PG version number readily available in Make

Make numeric form of PG version number readily available in Makefiles.

Expose PG_VERSION_NUM (e.g., "90600") as a Make variable; but for
consistency with the other Make variables holding similar info,
call the variable just VERSION_NUM not PG_VERSION_NUM.

There was some discussion of making this value available as a pg_config
value as well. However, that would entail substantially more work than
this two-line patch. Given that there was not exactly universal consensus
that we need this at all, let's just do a minimal amount of work for now.

Michael Paquier, reviewed by Pavel Stehule

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/a5d489ccb7e613c7ca3be6141092b8c1d2c13fa7

Modified Files
--------------
configure | 2 ++
configure.in | 1 +
src/Makefile.global.in | 1 +
3 files changed, 4 insertions(+)