IT HAS BEGUN!

Remove 1.8 tests and stdlib and start migrating boot logic toward
a single runtime compatibility mode.
Eliminate calls to Ruby.is1_8 and is1_9.
Oopsed one line that should not be there for 1.9+.
Remove some remaining version-switching nuggets.
Revert "Move exitedException capture above other logic, to ensure it sets."

This reverts commit be4d7212a1bc7e5d516d7d1d6f757d3b34d8d8cd.
Revert "Always log unhandled exceptions in threads."

This reverts commit 79423216e3aa3ed0dc377aa1998471be02845613.
Remove --<version> flag from mspec runs.
Move to 2.0 versioning and line up tests.
Get all suites in test:extended passing.
Unify spec tags and get rubyspec passing under 2.0 mode.
Tidy up spec run in travis a bit.
Merge branch to support only a single Ruby compat mode.