xserver tslib and 3600_ts detection

[Bas Mevissen]

Hi,

The current configure script of xserver detects if it needs to configure
for a touch screen only by the presence of header files.

So this may (and does) easily lead to incorrect #define of the symbol
TOUCHSCREEN because these header file(s) just do exist in your kernel
source tree.

To resolve this, I would like to propose to add two switches:

--disable-tslib (default: auto)
--disable-ts_3600 (default: auto)

Is this a good idea?

Regards,

Bas.