add unit tests for wm_receiver
add wm-sender tests
Merge branch 'master' of github.com:kylewm/redwind
twitter plugin: expand URLs using twitter's supplied entities rather
than following redirects for each one.

unfortunate side effect, other url shorteners are preserved now :(

cc: @thedod thanks for the heads up!
wm_sender_test, fix failing test by mocking a hell of a lot of urllib
travis config: remove reference to obsolete reqs