Upgrade and patch ultisnips.

I tried upgrading, but that didn't fix the issue.  Then I got it into a repeatable state. :-)  This fixes the issue I've been seeing, and I've brought it up in SirVer/ultisnips#171, but I'm not sure if the approach will be acceptable or not upstream--I hope it is.  You can see more of the gory details [there](https://github.com/SirVer/ultisnips/issues/171#issuecomment-63033020), if you like. :-)