Tweak search_path inline when creating topology extension

Also fixes postgis website url and "make clean" rule.
NOTE: I found that AddToSearchPath code is duplicated, might be
      a good idea to drop one of the two implementations (both
      touched with this commit)

git-svn-id: http://svn.osgeo.org/postgis/trunk@12504 b70326c6-7e19-0410-871a-916f4a2858ee