[SVN] Extended mode for regexps in language grammars

[Myles Byrne]

I'm having trouble activating extended mode for regexes in language
grammars. As soon as I turn extended mode on the expression fails to
match.

I've isolated the problem in this gist:
https://gist.github.com/24b357a08eb8f3ccca4b

Please let me know if you need any more information or have some idea
of what I'm doing wrong.

Thanks,

-- Myles