Autojoin channels are rejoined after reconnection if all channels were closed

[flashcode]

When all channels of a server are closed (/buffer close), a reconnection to the server (with /reconnect or after a network disconnection) will rejoin all channels in .autojoin option.
But if at least one channel was still opened, the reconnection will not rejoin other channels in .autojoin option.
Expected behavior: never rejoin new channels on reconnection but only currently opened channels.

Reported by Boobuigi_ on #weechat.

Bug on Savannah: https://savannah.nongnu.org/bugs/?21529

[mkoskar]

I would suggest to:

• keep /connect and /reconnect behaviour as is; it processes .autojoin (if set) by default + rejoins all channels in opened buffers; if -nojoin is passed no channels are autojoined or rejoined
• create configuration option irc.(server_default|<server>).autoreconnect_autojoin (on - default / off); on - when auto-reconnecting process (or don't in off case) autojoins (if set)