Engine-XMPP: wasn't able to close unsynced (not fully joined) mucs

in case of long delays this could easily happen
also, regression-danger due to nonexisting chat windows that the server might send messages for
Engine-XMPP: a server<->client race condition could cause a closed chat to be joined

now this kind of chat is automatically closed and an error message is displayed in the protocol chat
this required a refactoring of OnGroupChatPresenceError because that function expected a non-null XmppGroupChatModel
Engine, Frontend-GNOME: restored ABI compat with smuxi-servers < 0.8.11 (closes: #893)
Merge branch 'stable'
Merge pull request #167 from knocte/master
Build: bumped version to 0.11
Frontend-GNOME: fixed website link in about dialog showing error on Windows
Merge branch 'stable'
Frontend-GNOME: fixed NRE thrown in ChatTreeView.IsVisible() (closes: #919)

Seems like TreeView.GetVisibleRange() returns false and doesn't set the out
parameters when the treeview is not visible/realized. This happened on
Ubuntu/Quantal where the treeview is not expanding to its preferred size for
some reason.
Merge branch 'stable'
Frontend-GNOME: allow wrapping to first/last from last/first chat

This restores the behavior of with tabs which allowed wrapping from the last tab
to the first tab and from the last tab to the first tab.
git-contributors: don't count merge commits
Frontend: populate CMD* hook variables for command-manager hooks
Merge branch 'stable'
Engine: added CMD_CHARACTER to command hook environment
Merge branch 'stable'
Engine-IRC: added translator hint for "Queuing joins" msg string
Engine-IRC: fixed already joined detection of /join command (closes: #921)
Frontend: fixed potential NRE with commands issued from command hooks
Engine-JabbR: fixed potential NRE in CommandHelp() when issued from hooks

CommandModel.FrontendManager is null when issued from hooks