Fix two-finger tap on macOS with Tk9

[windymilla]

With Tk9, 2-finger tap is generating mouse 3, whereas it
generated mouse 2 with Tk9. Bind both of these, so it
should work with either Tk version.

Testing of debug version:
In Tk9 environment, and Tk8 environment, do two-finger tap on main text window, then look at output in the terminal window. Compare with Ctrl-click.

[srjfoo]

ctrl+click got nothing on either Tk 8 or 9. (In other apps, ctrl+click and two-finger tap with my system setup get the same response.)

Tk8 two-finger tap: <ButtonPress event num=2 x=199 y=298> is typical, where the x/y coorinates change depending on where the touchpad pointer is located.

Tk9 two finger tap: <ButtonPress event num=3 x=199 y=298>, ditto.

Go figure? 🙄