Fix multitouch evdev input probing

Multitouch devices that do not support single touch protocol
were detected as "user input only" sources. Fixing this allows
mce to ignore touch events when appropriate.

[mce] Detect also multitouch only devices as touchsreens
Do not use optional ABS_MT_TOUCH_MAJOR for multitouch detection

ABS_MT_TOUCH_MAJOR is not a mandatory feature for the multi-touch protocol,
and may be missing in some implementations.
Merge pull request #47 from spiiroin/multitouch_probe

Fix multitouch evdev input probing