Fix a few remaining tz naive dates

And remove redundant but != date parsing methods. In process make
the general parsing function less lenient (don't default date nor
month)
Merge branch 'dhm/timeconv/bug0' of github.com:edx/edx-platform into dhm/timeconv/bug0

Conflicts:
	common/lib/xmodule/xmodule/fields.py
	common/lib/xmodule/xmodule/timeinfo.py