send SIGQUIT/SIGTERM only once to the workers

there is no need to send more than once the signal to the workers when
exiting. With this patch we are sending once the QUIT/TERM signal and  then
wait until the graceful timeout or until there are workers alive.

fix #655
fix run loop in sync worker
remove dynamic timeout temporarely

this change is removing the dynamic timeout to make it sure it doesn't have
any side effect in the worker monitored like reported in #942
Rename `GeventResponse.response_length` to `sent`

This makes it compatible with the duck typing of the response object
in the glogging request logger.
Merge pull request #959 from benoitc/test/gh942-remove-timeout

remove dynamic timeout temporarely
Let the reloader kill the worker by signal only

There is no reason to raise a `SystemExit` because the reloader thread
will die when the worker exits anyway. Having this exception can cause
tracebacks during interpreter shutdown (#910).

Close #910
Merge pull request #960 from benoitc/fix/910-reloader-tracebacks

Let the reloader kill the worker by signal only