evdev: Log evdev event queue overflows

Log a message when the kernel event queue overflows and events are dropped.
After 10 messages logging stops to avoid flooding the logs if the condition
is persistent.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
filter: Fix typo

accelator -> accelerator

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
filter: perform speed computations with doubles

Converting to integer before the sqrt calculation can cause loss of
motion at low speed.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
evdev: add DPI to evdev calculations

Assume "normal" mice are 400DPI, and that all calculations should be
normalized to this before being fed into the filter.

There isn't yet a way to configure a device's DPI.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>