(Qconnect, Qfailed): New variables.

(Qconnect, Qfailed): New variables.
(syms_of_process): Intern and staticpro them.
[NON_BLOCKING_CONNECT]: New conditional.
(connect_wait_mask, num_pending_connects): New variables.
(status_message): Convert Qfailed status.
(Fopen_network_stream): Added support for non-blocking connect.
New optional args: filter, sentinel, non_blocking.  Doc updated.
[HAVE_GETADDRINFO, !HAVE_GETADDRINFO]:  Merged common code.
(deactivate_process): Handle pending non-blocking connect.
(wait_reading_process_input): Poll for status of non-blocking
connects.  Exec sentinel directly when connect succeeds.
(status_notify): Don't read process output if not yet connected.