[Maxima] maxima-el: feature suggests

[Jay Belanger]

I know we're doing prereleases now, but the keybinding change at least
includes a bug fix.  
Anyhow, the prompt in inferior-maxima-mode is now read-only, and in
the Maxima related buffers, the following keybindings are in effect:
C-cC-dh    Get help on a prompted-for topic
C-cC-dd
C-cC-dC-d  Get help with the symbol under the point
C-cC-da
C-cC-dC-a  Apropos
C-cC-dp
C-cC-dC-p  Apropos for the symbol under the point
C-cC-dm
C-cC-dC-m
C-cC-di
C-cC-dC-i Read the info manual.

Jay