make distclean patch from Andy Armstrong.

make distclean patch from Andy Armstrong.
(Distclean isn't perfect yet because there's a spurious directory tree
created but not cleaned up by ext/Test/Harness/t/harness.t, but Andy is
working on fixing the cause)
No idea about the state of play of disclean on VMS - I couldn't see how
or where to add the three extra directories to it.

p4raw-id: //depot/perl@34640