add failed test case relates #41
always store and compare lowercase email addresses - closes #41
fix email validators definition

- fix for transaction in tests
fix cases, where value fed or get from email field is None
replace basestring with pyramid.compat.string_types in comparator
Merge pull request #42 from fizyk/bugifx/41-make_email_case_insensitive

Bugifx/41 make email field case insensitive