[PATCH] Support Carbon-specific package paths.

[Stephen J. Turnbull]

Aidan Kehoe writes:

 > That allows the pure Mac people to be conscientious and Mac about their work
 > habits, and the mixed Unix-Mac people to reasonable behaviour by default.

And leaves the XEmacs Dev Team holding the bag.  "Not finding your
packages?  Where are they?  Oh, this is a *Mac*, so on odd Tuesdays of
months with a 'u' in them it's in .xemacs ... what day did you say it
is again?"

I think it's a bad idea to be too smart for anybody's good on this
kind of thing.