Solr backend upgraded to Solr 4

[bigjust]

Hello all,

I merged my solr4 branch into master, which has the following implications:

1.  I updated tox to test django 1.5 and 1.6 (the current beta tarball), and it uses the py26, py27, py33, pypy python implementations.

2.  There are currently tests that fail, but are all solr-upgrade related.  They are the content extraction test which i'm almost certain is a test config issue, and the spatial tests, which is due to a implementation change between solr 3 and solr 4.  These will have to pass before a release can be made.  But I thought it would be good to get the rest of the changes in master so that other people can dissect and suggest/make changes.

I'll slowly be updating the docs over the weekend, and trying to fix the tests, but i'll be on irc if anyone wants to help.  You guys keep being awesome!

-- Justin

PS. I have a vagrant file and base box (http://www.vagrantup.com) that I use as a test bed for running the test suite if anyone is interested.  It's basically just debian 7 with solr and elasticsearch configured and running. I'm also thinking we should get travis-ci up and running again.