[9fans] chords for 2-button mice

[miller@hamnavoe.demon.co.uk]

Plan 9 mouse drivers allow a 2-button mouse to impersonate a 3-button mouse
by interpreting shift + right button as middle button.  However, chords
are a problem because shift + left button + right button is still
interpreted as left button + right button.  The following one-line change
to the kernel causes shift + left button + right button on a ps2 mouse
to be interpreted as left button + middle button, which makes acme and
rio much more comfortable on my mouse-challenged thinkpad.

term% diff /sys/src/9/pc/mouse.c mouse.c
62c62
< 	static uchar b[] = {0, 1, 4, 5, 2, 3, 6, 7, 0, 1, 2, 5, 2, 3, 6, 7 };
---
> 	static uchar b[] = {0, 1, 4, 5, 2, 3, 6, 7, 0, 1, 2, 3, 2, 3, 6, 7 };

I believe the following change does the same for serial mice, but I haven't
tested it:

term% diff /sys/src/9/port/devmouse.c devmouse.c
549c549
< 	static uchar b[] = { 0, 4, 1, 5, 0, 2, 1, 5 };
---
> 	static uchar b[] = { 0, 4, 1, 5, 0, 2, 1, 3 };
589c589
< 	static uchar b[] = {0, 4, 2, 6, 1, 5, 3, 7, 0, 2, 2, 6, 1, 5, 3, 7};
---
> 	static uchar b[] = {0, 4, 2, 6, 1, 5, 3, 7, 0, 2, 2, 6, 1, 3, 3, 7};

(Note to Vita Nuova: I think this is applicable to Inferno as well.)

-- Richard Miller