Partially revert r17180

It changed the behaviour of _postgis_pgsql_version
Now uses the appropiate 5-6 digit version from server_version_num

References #4296
References #4303



git-svn-id: http://svn.osgeo.org/postgis/branches/2.5@17206 b70326c6-7e19-0410-871a-916f4a2858ee
1 job for svn-2.5 in 22 minutes and 46 seconds
Status Job ID Name Coverage
  Test
passed #149134071
test

00:22:46