[#299] Clear up changes to Pylons' config between tests

We also, instead of always loading test.ini in these tests, we use whatever Pylons loaded.
[#299] Reload AuthFunctions if couldn't find the action we're looking for

The problem I found was when you're testing a bunch of things
sequentially. Then, the first time that method is called, it
loads all known AuthFunctions and puts into a cache. Then it
only checks that cache.

But what happens if some code, after this has happened, adds
a new AuthFunction? It never gets added to the cache.

With this change, if we have the requested function on cache,
we use it. If not, we refresh the cache and see if something
changed.
[#299] Clear test data after each test is run

This might not be the best way to do it. It's too repetitive, but it's
better than leaving trash behind.

We might investigate running the tests inside a transaction, and rolling
back when we're done (is it done already?).
[#299] Run ckan and ckanext tests on Travis
[#299] Fix ckanext.{json,pdf,recline}preview tests

The problem is that we were looking for each *_preview.js, when the included
files are already minified (*_preview.min.js).
#299 clear action cache when plugin loads
#299 unload and load datastore plugin at correct times
Revert "Run DataStore tests in Travis-CI"

This reverts commit 76cc9d3b8641489dc8e6674cb0e46ade02ce0b25.

Conflicts:

	.travis.yml
[#299] Don't call WHERE statements if there're no terms

This removes the following warning:

/home/vagrant/pyenv/local/lib/python2.7/site-packages/sqlalchemy/sql/expression.py:1925:
SAWarning: The IN-predicate on "term_translation.term" was invoked with an empty sequence.
This results in a contradiction, which nonetheless can be expensive to evaluate.
Consider alternative strategies for improved performance.
309 no private datasets in activity streams, revisions, group listing and tag listings
make group_list_dictize reasonably fast by going through search index
[#309] add package count using search index
[#345] Also recognize driver `postgres` in `engine_is_pg`
[#309] Tidy up a couple of comments

No point in putting "TODO" comments in the source code no one will
remember to go back and do them and the comment may become outdated/misleading.
[#285] Remove code in base controller that is not used in the ckan codebase
[#285] Re add function mis-used in api controller
[#285] _make_unicode() still has user
[#285] Move function into only function using it
[#285] Move function into API controller as only user
[#285] Fix missing imports