Add very rough and ready support for sentry as proof of concept.
Fix intermittent riak search test failure.
Model migrations.
Better migration machinery.
Merge branch 'develop' into feature/issue-301-riak-model-versioning
Merge branch 'develop' into feature/issue-301-riak-model-versioning
Merge branch 'develop' into feature/issue-301-riak-model-versioning

Conflicts:
	vumi/persist/tests/test_model.py
moving old tests to use the newer TransportTestCase baseclass
work in progress
encode unicode headers as utf8 bytestrings
stray print
encode Indexes better when given tuples
less code
Merge branch 'develop' into feature/issue-381-txriak-manager-bytestring-headers
Merge branch 'feature/issue-381-txriak-manager-bytestring-headers' into develop
wrapper for zrangebyscore in txredis
Shuffle riak_search stuff and add riak_search_count.
Some test cleanup.
Break up long test.
First part of throttle-handling.