standard event bindings

[Jim Kingdon]

> I therefore mapped KP + and KP - to zoom in and out in the mac
> (non-Tcl) interface a long time ago. Maybe we should do this as a rule
> on all platforms

Well, it is kind of bad to have it be a Mac-only thing.

> get rid of the curly braces altogether?

Unfortunately, this doesn't work so well either.  All the keyboards I
use (for example, laptop keyboards) don't have a convenient keypad (it
involves using a Fn key or a "keypad" mode or some such).

I can't help but think there is a simpler solution.  Usually in tcl,
if one has confusion between "{}" as "{" and as empty string, it has
to do with getting quoting wrong.  Seems to me (as far as I can tell
from the bind(n) manpage) that "%K" is wrong and it should be just %K.
In tcl, {} are quotes, so I think what is happening is that tcl quotes
for you and then the "" quote it again, so it then does become
impossible to distinguish between "{" and an empty string.  I haven't
tested this hypothesis, though.

I also might move the if statement inside handle_key_binding but I
doubt that has a particularly strong connection to this problem.