Non-Commutative calculations in Calc, Revisited

[Neon Absentius <absent@sdf.lonestar.org>]

When in non-commutative (aka `matrix') mode calc calculates 
(a b)^-1 to be a^-1 b^-1 instead of the correct b^-1 a^-1.

Actually there is a more general bug.  It calculates (a b)^n 
to be a^n b^n.  I think this rule should be removed when a and 
be don't commute.  Furthermore a special rule should be included 
that deals with the case n=-1. 

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