yarddoc wasn't picking up Hash core_ext documentation because of the trailing unless; diff best viewed with -w.
Apply same treatment to String core_exts as we did to Hash ones to get them to show up in YARD (they still don't, but at least we have consistency?); Fixes bug like #1036 with String, ensures that our constantize extension only gets added if it isn't present already. Best viewed with -w.
Merge pull request #1078 from yaauie/yarddoc-vs-coreexts

Yarddoc vs coreexts