Add blockers to process functions

Add blockers to process functions

* src/process.c (set-process-filter, set-process-window-size,
process-contact, process-datagram-address, set-process-datagram-address,
set-network-process-option): Make functions wait (block) on network
process until pending DNS requests have been processed and associated
socket initialized.

* src/process.c (process-send-region, process-send-string,
process-send-eof): Make functions wait (block) while network process is
in connect state.