Add support for regex_t->re_nsub struct member

Howdy,

I was wondering if you'd like to add support for the re_nsub struct member of regex_t to your module so that the number of capture-groups can be determined after compiling a regex.

Attached is a patch to do just that.

Thanks for your work!

Cheers,

--
Matthew Horsfall (alh)
http://dyn.com