Merge pull request #139 from mbj/fix-warnings

Fix shadow local variable warnings
+ ruby-rewrite: add a --modify switch for rewriters that modify AST (fixes #143).
* parser/current: fallback to latest released Ruby instead of raising (fixes #140).
- lexer.rl: don't fail to parse string literals in huge files (fixes #142).
test/test_current: extend to 2.1.1.
Fix 1.8 compatibility.
Fix warning in lexer