fix 'multiple repeat' error from regex for c++ filetypes

[juliantaylor]

unescaped ++ is invalid regex causing easytag to fall back to the
vimscript highlighting which does not split the regex into small chunks
that vim can handle.

[xolox]

Thanks for spotting the bug and contributing a fix! During the merge I changed the relevant line to use re.escape(). That way no matter what funky characters are embedded in file type names, it will work regardless. That's how I should have done it the first time around, but evidently it didn't occur to me back then :-). Happy Vimming!