Avoid unnecessary db query on index update

pks_seen is only needed if objects are removed from
index, so only compute it if necessary.
Improve pks_seen to not build an intermediary list.
Added some faceting tests for ElasticSearch.
More ElasticSearch test fixes.
Added a spelling test case for ElasticSearch.
Fixed my own spelling test case. How embarrassing.
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.
fixed basepython for tox envs, thanks --showconfig

also, added latest django 1.4 release, which doesn't error out
currently.

Downgraded python3.3 to python3.2, as thats what the lastest debian
stable includes.  I'm working on compiling pypy and python3.3 on the
test box, so those will probably be re-added as time allows.

failing tests: still solr context extraction + spatial
Fixed autocomplete() method: spaces in query
added test for autocomplete whitespace fix
removed python 1.4 / python 3.2 tox env because thats not possible

also pinned versions of requirements for testing
Fixed #575 & #838, where a change in Whoosh 2.5>
required explicitly setting the Searcher.search() limit
to None to restore correct results.

Thanks to scenable and Shige Abe (typeshige) for
the initial reports, and to scenable for finding
the root issue in Whoosh.
Fix documentation regarding ModelSearchIndex to match current behavior

Closes #606. Thanks to @bradleyayers for the report.
Remove bit about SearchQuerySet.load_all_queryset deprecation

That method was entirely removed in commit b8048dc0e9e3.

Closes #607. Thanks to @bradleyayers for the report.
Merge pull request #881 from benspaulding/docs/issue-606

Fix documentation regarding ModelSearchIndex to match current behavior
Merge pull request #882 from benspaulding/docs/issue-607

Remove bit about SearchQuerySet.load_all_queryset deprecation