ycmd watchog timer now wiser about machine sleep

We now make sure we don't terminate ycmd if we skipped a watchdog wakeup
time. If we skipped a check, that means the machine probably went to sleep and
the client might still actually be up. In such cases, we give it one more wait
interval to contact us before we die.
Merge pull request #903 from Valloric/watchdog-fix

ycmd watchog timer now wiser about machine sleep