Provide Genode version information in log

Fixes #551
os: reprogram timer solely if needed

If an alarm/timeout object became head of the timeout queue, then the
low level timer must be reprogrammed.

Issue #1106
timer: fix wrap handling for x86 PIT

Issue #1106
timer: fix corner case if counter is 0

If counter drops to 0, the wrap flag is set also. That means we have actually
no wrap around. The patch avoids to add too much time to the elapsed time
variable.

Issue #1106
pit: no lock required in pit anymore

timer service calls platform timer nowadays solely from the vary same thread
 - the entrypoint of the timer service

Issue #1106