Vim: get Command-T to re-use existing windows/tabs

Based on the new options added in commit 0f4c700ddf2b1 (and documented
in 00651aff01bd8), let's make selecting items re-use existing
windows/tabs when possible.

I might actually look at making this the default behavior in Command-T
whenever the `'switchbuf'` option is present and appropriately set; but
for now, let's just try this out locally.
Vim: update Command-T to latest "next"

* .vim/bundle/command-t 9db519e...925cf02 (4):
  > Merge branch 'ton/clear-statusline' into next
  > Change a `#each` + `#<<` to a `#map`
  > Merge branch 'rabidpraxis/implement-ctrl-w' into next
  > Update Git .mailmap file