Change made to elog:

o  Change all current CVS messages of NOTICE to WARNING.  We were going
to do this just before 7.3 beta but it has to be done now, as you will
see below.

o Change current INFO messages that should be controlled by
client_min_messages to NOTICE.

o Force remaining INFO messages, like from EXPLAIN, VACUUM VERBOSE, etc.
to always go to the client.

o Remove INFO from the client_min_messages options and add NOTICE.

Seems we do need three non-ERROR elog levels to handle the various
behaviors we need for these messages.

Regression passed.