PostGIS: Add the prefix for the coordinate system name

[sunch]

In the past, we took value from the spatial_ref_sys:srid column as the coordinate system name. Actually, it's not exactlly right to do this. The returned 'srid' is just the ID of the spatial reference system as defined by the autority cited in the auth_name column. ​http://postgis.org/documentation/manual-svn/ch04.html#spatial_ref_sys

So it needs to set the value from auth_name as the prefix of the srid to compose the intact CS name.