[PATCH] server_version_num should be GUC_REPORT

Hi all

While looking into client code that relies on parsing server_version
instead of checking server_version_num, I was surprised to discover that
server_version_num isn't sent to the client by the server as part of the
standard set of parameters reported post-auth.

The docs reflect this:

http://www.postgresql.org/docs/current/static/protocol-flow.html#PROTOCOL-ASYNC

The attached patch marks server_version_num GUC_REPORT and documents
that it's reported to the client automatically.

(See mention here:
https://github.com/impossibl/pgjdbc-ng/commit/40b6dc658a9b38725be220e2fa653a5a8a0cbae4#commitcomment-8427979)

--
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services