Fix crash on save when icc_profile is None
Cleanup handling of ICC profile, more extensive testing
don't use bare asserts, don't mask file builtin with local
Tightened up the tests
Merge branch 'no-icc-profile' of github.com:wiredfool/Pillow into no-icc-profile
Merge pull request #508 from wiredfool/no-icc-profile

Fix crash on saving PNG when icc_profile is None