(BUGFIX) sn_rcs_discard would break sn if rcs wasn't installed
(BUGFIX) The dialogs shouldn't appear when the version control programs aren't there

When, for example, rcs isn't installed, sn would show an error saying
the program was no there but then it would proceed to the check-out, or
whatever, dialog.
Merge branch '8.4' into Ttk

Conflicts:
	CHANGELOG