More hard-coded version numbers reduction

This commit fixes raster and postgis/raster extension.
I noticed that the extension files have what looks like being
an attempt to compute the "previous" version in another way,
but haven't tried to use those variables. Also, I think it would
be worth moving all the version strings into the Version.config
file in top-level. Not done by this commit, but comments left

git-svn-id: http://svn.osgeo.org/postgis/trunk@12036 b70326c6-7e19-0410-871a-916f4a2858ee
Use a different diff file for each tested shapefile output file

Hopefully fixes #2507 (permission denied on overriding a tmp file)

git-svn-id: http://svn.osgeo.org/postgis/trunk@12037 b70326c6-7e19-0410-871a-916f4a2858ee