[asan] enable detect_odr_violation=2; https://code.google.com/p/address-sanitizer/wiki/OneDefinitionRuleViolation . This feature has been working quite well so far, found a few bugs and zero false positives. The main problem is that there could be lots of true positives and users will have to disable this checking until the bugs are fixed.
Implement one operator== with another.

Thanks for David Blaikie for the suggestion.