setOnce
IDFA property
use IDFA as default distinct id
use ODIN1 as fallback default distinct id
unified identify:
add ODIN as a lib
add $app_short_version_string
Merge branch 'master' of github.com:mixpanel/mixpanel-iphone

Conflicts:
	Mixpanel/Mixpanel.m
make unregisterSuperProperty: the same as other libs and tests
fix up tests