xinput --disable/xinput --enable fixes for synaptics

[Keith Packard]

You really don't want to know, but I was disabling/enabling synaptics
repeatedly during login on my new machine. I noticed that the X server
was slowing growing more and more fds attached to the device, then I
noticed that the device wasn't actually working, even if I did xinput
--enable.

The first patch closes the device when the DeviceOnHook fails:

 [PATCH 1/2] Close device if DeviceOnHook fails

The second patch fixes the evdev DeviceOnHook to not fail by making
sure libevdev has the new fd before we try to grab the device:

 [PATCH 2/2] When re-opening evdev, set the fd before trying to grab

-keith