[Engine-XMPP] Fixed build on Mono 2.6.7

TimeSpan.ToString(format) is .NET >= 4.0
[Frontend-GNOME] Prevent making Campfire connections to invalid hostnames (closes: #822)
Merge branch 'stable'
[Engine] Re-apply engine/volatile/persistent buffer lines settings when changed
[Engine] Added useful Trace.Call() to ChatModel.ApplyConfig()
Merge branch 'stable'
[Debian] Fixed build, jabber-net was replaced with agsxmpp
[Engine-XMPP] Fixed typo
[Engine-XMPP] Applied Coding Standards, handlers should always match the event name
[Frontend-GNOME-XMPP] Fixed build on Mono 3.0.6
[Engine-XMPP] Fixed header of "Advanced XMPP commands"
[Engine-XMPP] Don't hardcode the protocol name
[Engine] Added distinct MessageBuilder.MarkAsHighlight() method
[Engine-XMPP] Highlight subscription requests
[Engine*, Frontend-*] Removed help from help output

There is really no point in telling the user there is a help command when he is
already using the help command. Also the Smuxi tab is already telling the user
to use the /help command.
[Engine-XMPP] proper output for error messages
[Engine-XMPP] reset socket before reconnect
[Engine-XMPP] detect facebook and prevent facebook bugs
[Engine-XMPP] do not "update" PersonChat name if IdentityName didn't change

there is no update function for chats -> remove and recreate is not very nice, prevent it wherever possible
[Engine-XMPP] display "is now known as" message on IdentityName change