Add tox.ini for multi-version testing
add tox test environment for sqlite, and include elasticsearch
Python 2.6 compatibility - fixes #156
Merge pull request #208 from gasman/feature/tox

tox test environment and Python 2.6 support
Merge branch 'master' into search-changes

Conflicts:
	.travis.yml
	wagtail/wagtailsearch/backends/elasticsearch.py
	wagtail/wagtailsearch/indexed.py
	wagtail/wagtailsearch/tests/test_backends.py