Generic axis support in evdev

After the groundwork by Matt Helsley we now have generic axis support in evdev. So evdev finally sets the device up according to what the kernel reports rather than limiting itself to x/y and potentially pressure.

A truly generic driver. Rejoice.

And because we can, it does axis labeling too (if you have xserver git master, that is).
No more guessing what axis 7 actually is.

The obligatory "screenshot":

whot@roo:~> xinput --list-props "PIXART USB OPTICAL MOUSE"  | grep "Axis Labels"
 Axis Labels (242): "Rel X", "Rel Y", "Rel Vert Wheel"
whot@roo:~> xinput --list-props "Wacom Intuos3 4x6" | grep "Axis Labels"
 Axis Labels (242): "Abs X", "Abs Y", "Abs Z", "Abs Rotary X", "Abs Rotary Z", "Abs 
Throttle", "Abs Wheel", "Abs Pressure", "Abs Distance", "Abs Tilt X", "Abs Tilt Y", "Abs Misc"

Expect this to be in evdev 2.2, once it has matured and potential glitches are ironed out.