Recognize identical strings when B_TRANSLATE macro or context changes #74

Sometimes strings move from one source file to another, changing the B_TRANSLATION_CONTEXT. Or you see that an explanation would be helpful and change B_TRANSLATE to a B_TRANSLATE_COMMENT. With both changes, the actual strings don't change, but Polyglot doesn't recognize that and deletes the old translations...

I don't know if changing B_TRANSLATE to B_TRANSLATE_MARK or similar localization macros in code is the same, but I suspect so.

Would be nice if Polyglot became a bit more forgiving in these situations.