Create events table & handle setting claimed_time.
Track username changes, add /%username/events/ view.
Switch travis to postgres 9.3.
Try addressing comments from PR.
Merge branch 'master' into events

Conflicts:
	gittip/models/__init__.py
	gittip/models/participant.py
Fix up branch.py file; #2006

Not sure why this API changed. Something we did on master in the mean
time?
Fix bug in events page for #2006

The need for this import entered with #1369.
Merge pull request #2006 from gittip/events

Eating elephant, first step (events, db schema)