do an uninstall before an install

- the fact that this works when you're pointing at a package that
  isn't the same package that was installed, and technically could both
  be installed at the same time, hurts my brain, but it does appear
  to work.  windows is strange.
- if we don't do this we can wind up in a broken state with msis
  installed and when we run the first time we magically seem to get
  the old package re-wired up (again, hurts my brain), but the
  uninstall at the end fixes things so the second time through it will
  work.  by uninstalling here it should clean up old broken installs
  without needing a double-run.
- ow ow ow ow my brain hurts.