Allow for multiple attempts when reconnecting

Allow for multiple attempts when reconnecting

* doc/misc/rcirc.texi (rcirc commands): Mention rcirc-reconnect-attempts
* etc/NEWS: Document change
(rcirc-connect): Ensure no other process exists
(rcirc-reconnect-attempts): Add option
(rcirc-failed-attempts): Add local variable
(rcirc-reconnection-timer): Add local variable
(rcirc-reconnect): Add function
(rcirc-sentinel): Manage multiple reconnection attempts
(rcirc-process-server-response): Change user for error messages
(rcirc-mode): Don't set rcirc-last-connect-time
(reconnect): Extract functionality to rcirc-reconnect