Disable canvas_login=1 when not forced.

We were always sending canvas_login=1. This parameter
is only for when admins/support want to login using the
normal canvas login and school's use their own fancy sso/ldap
or what-have-you.
Merge remote-tracking branch 'instructure/CanvasKit/master'

Conflicts:
	CanvasKit/Networking/CKIClient.m
Merge pull request #33 from jarsen/master

Disable automatic forced canvas login