Less special-casing and code more in line with 'normal' index creation.

On PostGIS < 2, geometry_columns is a table that was manually maintained.
It's a view on PostGIS 2.

Removed possible u'' prefixes on Python 2.

http://bugs.python.org/issue28082

http://bugs.python.org/issue15767

Fixed #27211 -- Made UpdateCacheMiddleware include caching headers for "304 Not Modified" responses.

Thanks juntatalor for the initial patch.

Thanks Tim Graham for the regression test.

Thanks Tim for the review.

Thanks Valentin Ignatyev for the report.

Also test it on PostGIS raster fields.

Thanks Akshesh <aksheshdoshi@gmail.com> for help with the PostgreSQL query.
Thanks Tim Graham for the review.