update tox to test pypy, py26, py27, py33, django1.5 and django1.6

django 1.6 doesn't actually work yet, but there are other efforts to get that working
pass `using` to index_queryset for update
Update solr schema template to fix stopwords_en.txt relocation

Seems that in versions >3.6 and >4 stopwords_en.txt moved
to a new location. This won't be backwards compatible for
older versions of solr.

Addresses issues #558, #560
In addition, issue #671 references this problem
switch solr configs to solr 4

almost all tests passing, but spatial not working
[tox] run tests for 1.6, fix test modules so they are found by the new
test runner.

These changes are backwards-compatible with django 1.5.  As of this
commit, the only failing tests are the Solr extractraction test, and the
spatial tests.
fixed simple backend for django 1.6, _fields was removed.