Patch by Joshua Moore-Oliva.

Tulip issue #206:  In debug mode, keep the callback in the representation of
Handle and TimerHandle after cancel().

There is a race condition in create_connection() used with wait_for() to have a
timeout. sock_connect() registers the file descriptor of the socket to be
notified of write event (if connect() raises BlockingIOError). When
create_connection() is cancelled with a TimeoutError, sock_connect() coroutine
gets the exception, but it doesn't unregister the file descriptor for write
event. create_connection() gets the TimeoutError and closes the socket.

If you call again create_connection(), the new socket will likely gets the same
file descriptor, which is still registered in the selector. When sock_connect()
calls add_writer(), it tries to modify the entry instead of creating a new one.

This issue was originally reported in the Trollius project, but the bug comes
from Tulip in fact (Trollius is based on Tulip):
https://bitbucket.org/enovance/trollius/issue/15/after-timeouterror-on-wait_for

This change fixes the race condition. It also makes sock_connect() more
reliable (and portable) is sock.connect() raises an InterruptedError.

Don't raise a TimeoutError if we reached the timeout and the future completed
in the same iteration of the event loop. A side effect of the bug is that
Queue.get() looses items.

which now raise an exception if the socket is blocking.

sock_accept) of the proactor event loop don't raise an exception in debug mode
if the socket are in blocking mode. Overlapped operations also work on blocking
sockets.

the transport because SSL transport closes the old socket and creates a new
SSL socket object.

Remove also the _SelectorSslTransport._rawsock attribute: it contained the
closed socket (not very useful) and it was not used.