+ Translated some fixes across 1.8 and 1.9 from 2.0.
- Fixed some oddity where 1.9 lexing was blowing up on "0o". Seems invalid now.
- Either found a bug in MRI and/or fixed paren_nest count for []=? methods.
- Fixed lexing of heredocs vs chevron for some lex_states.
- Fixed lex_state transition for 1.9 if we lexed a defn name. Only 1.8 is odd.
Default lexer tests to 2.0... why not...

[git-p4: depot-paths = "//src/ruby_parser/dev/": change = 8739]