Arrow keys not working on qt terminal for Mac OS X

[Jun T. <tak...@kb...>]

On Mac OS X, the arrow keys (Left, Right, Up, Down) do not work
on qt terminal.

The reason is simple; Apple considers the arrow keys as part of keypad.
The Qt::KeypadModifier bit of event->modifiers() is set when I hit
the arrow keys.

Two possible patches are attached.
Only one of them (not both) should be applied.

If mouse.c is patched, then a user should use
bind KP_Left ...
to customize the binding of the Left-arrow key.
If, on the other hand, QtGnuplotScene.cpp is patched, then
bind Left ...
can be used. Maybe this is more intuitive for typical Mac users?