minibuffer prev/next bindings in calc "algebraic-entry" mode

[Miles Bader]

One long-standing complaint I've had about calc's "algebraic-entry" mode
(invoked by the ' key) is that the standard minibuffer prev/next
commands, M-p and M-n, don't work.  I later realized that the arrow keys
_do_ work, but as I normally never ever use them in the minibuffer, it
took me a _long_ time to find that out...

The algebraic-entry mode has it's own sort of half-assed
previous-command binding (bound to '), but it's not very good.

It also binds M-p to a fairly useless command, which basically just inserts 
"+/-".

I think for consistency and the sanity of our users, M-p and M-n should
have the standard bindings in this mode.  The existing mode-specific
binding of M-p doesn't seem useful enough to preserve (it could be moved
to a different key, e.g. M-+ or something if people actually use it for
something).

-Miles
-- 
Yo mama's so fat when she gets on an elevator it HAS to go down.