Patch by Michael Scharf. He writes:

The module cmd requires for each do_xxx command a help_xxx
    function. I think this is a little old fashioned.

    Here is a patch: use the docstring as help if no help_xxx
    function can be found.

[I'm tempted to rip out all the help_* functions from pdb, but I'll
resist it.  Any takers?  --Guido]