Fixed up that debian watch file, appears to actually work

Well that was a helluva lot harder than it should've been. Honestly, I
appreciate the flexibility, but it's hard to do something *simple*!

In case I ever need to revisit:

* This person's uversionmangle was the final fix I needed:
  https://lists.debian.org/debian-devel/2011/12/msg00535.html

* This is kinda understandable and helpful:
  http://eriberto.pro.br/blog/?p=1459

* Canonical docs are sorta okay: https://wiki.debian.org/debian/watch