deprecating the dispatch function

[John W. Eaton]

Given that we now have @-style classes available in Octave, is there
any objection to deprecating the dispatch function?  Eventually
removing this feature would simplify function lookup in the symbol
table, and I see no reason to have two methods of doing approximately
the same thing, especially when the way it is done with dispatch is more
limited.  If there are no objections, I will mark the dispatch
function as deprecated for the 3.4 release.

jwe