click-handler-mixin

[lynch@aristotle.ils.nwu.edu]

I would like to suggest that click-handler type functions be factored out
of dialog-item, similar to the way key-handlers have been.

Pros:
  Make clicking code more modular.
    Easier to provide functions that would standardize highlighting.
    Could standardize the calling sequence for click/track/release at
LISP-level
  Slightly faster to check shorter list of clickable objects.

Obviously, this is not something to even think of for 2.0, but please put
on list of considerations for 2.1.

Disclaimer:  This comes about as a result of "dead space" on some of my
windows.
For a *long* time, I couldn't figure out why the space was dead...
Last night I realized:  The invisible help balloons [custom color sub-views
that display only on demand] were catching the clicks and promptly ignoring
them.

Thanks

PS  Will be posting said code after I patch point-in-view-p for help
balloons.
"TANSTAAFL" Rich lynch@ils.nwu.edu