[rst mode] Fixed minor bug: HTTP path with commas now properly highlighted

Hi marijnh,

I've discovered a minor bug in link highlighting w.r.t. rST : Apparently it is possible to have links with a comma inside (at least in the path portion). Had missed that in the previous commit; fixed now.

(Sorry for last pull request: did not now that GitHub closes a pull request, if a delete the corresponding branch before you've actually performed the merge op).