Implementing the "-d" flag
Adding a few more "-d" flag details after reviewing MRI

which unfortunately aren't part of the rubyspec suite.  Perhaps I should
add them there, too...
$DEBUG is off by default.  Le duh.
Merge remote-tracking branch 'upstream/master' into implement-d-flag
Merge pull request #457 from modcloth/implement-d-flag

Implementing the "-d" flag