Change deprecation warning to raise a WARNING after 2 version deprecation time

I kept the DEBUG for the first deprecating version to keep changes
small (no need to change testsuite again) but I really think
it should be at least a NOTICE in that case, or nobody would notice.

See #2440

git-svn-id: http://svn.osgeo.org/postgis/trunk@11988 b70326c6-7e19-0410-871a-916f4a2858ee
Add deprecation WARNINGS for functions deprecated 1 version ago

NOTE: it means a full version cycle with non-warned deprecations

See #2440

git-svn-id: http://svn.osgeo.org/postgis/trunk@11989 b70326c6-7e19-0410-871a-916f4a2858ee