Spawn RPC callbacks in dedicated greenlets.
GeventLibrary: disconnect remote services before stopping.

I'm not sure this is actually useful for something, but it seems
to be better behavior anyway.
Remove old _step() method.
GeventLibrary: discard messages longer than a threshold (100K).

To prevent DOS attacks.
Delete some comments that do not apply anymore.

The autoreloading feature was in tornado.IOLoop, which we don't
use anymore. So, no need to close the socket on exec.
GeventLibrary: make sleep in run() interruptible, in case new events pop up.
Fix minor documentation and logging things.
GeventLibrary: remove some leftovers of the threaded RPC calls.