Add a TextMate scope for .pytb files

This is the scope that Atom uses for these files.
See https://github.com/atom/language-python/blob/master/grammars/python-traceback.cson
Merge pull request #1686 from github/pytb-tm_scope

Add a TextMate scope for .pytb files
Use MaskLexer for *.mask
Merge pull request #1678 from tenbits/master

Use MaskLexer for *.mask