Don't print traceback when no detailed diagnostic

We should only print the message.
More logging for extra conf store
Ensuring server cleanup on OS signals

atexit won't run registered functions for SIGTERM which we send to the server.
This prevents clean shutdown.

Also making sure that the server logfiles are deleted as well.
Resolving issues with event requests timing out

It appears that the issue comes from sending a None timeout to Requests. It
seems it's a bug in Requests/urllib3. So we just pick an arbitrary long timeout
of 30s as the default.
Tweaked the request retries logic.

We now send more retry requests that are less spaced apart.
Signal handler must take 2 params

Otherwise we get a TypeError
Removing unsupported signal() calls on Windows

SIGQUIT and SIGHUP are not supported.

For details, see Python docs: http://docs.python.org/2/library/signal.html#signal.signal
Nth attempt at correct shutdown procedure.

If we install an explicit signal handler for SIGTERM and SIGINT and then call
sys.exit ourselves, atexit handlers are run. If we don't call sys.exit from the
handler, ycmd never shuts down. So fixed... I think. We'll see.

Fixes #577... again.
Minor cleanup of Completer comments