Update Tcl/Tk to 8.6.3

- new file dialogs on Vista+
- tclWinTime.c was cleaned up a bit, and no
  longer uses 'timezone' (which is now _timezone
  in VS2015, so we get to avoid patching that
  file).
- rules.vc is patched in both Tcl and Tk sources
  to allow building with VS2015
Fetch new external sources on the buildbots
Backed out changeset ceaac3d483a1 (buildbots refreshed)