#2790 SET_VARSIZE redefined - to fix swapped out liblwgeom.h with liblwgeom_internal.h which includes reference to postgis_config.h to do conditional right thing based in pg version

git-svn-id: http://svn.osgeo.org/postgis/trunk@12704 b70326c6-7e19-0410-871a-916f4a2858ee