Eliminate File.exists? deprecation warnings on Ruby 2.1.0
Eliminate private attribute warning
Eliminate variable not initialized warnings
Silence method redefined warnings when reloading thorfiles

This silences the warnings when the Thor specs are run but will still
be there when used by the end user, so it may need revisiting if we
want to eliminate warnings when using Thor as well as when testing it.
Run specs with $VERBOSE = true
Eliminate undefined variable warnings on Ruby 1.8.7
Test on Ruby 2.1.0
Merge pull request #394 from pixeltrix/fix-warnings

Fix warnings when running specs with `$VERBOSE = true`