[Frontend-GNOME] Don't quit on NotImplementedException
[Build] better guess for the C# compiler available

There are some distributions that bundle only a limited set of class
libraries to be able to meet size requirements better. Such is the case
of Ubuntu, which normally ships with only the subset compiled for the
4.0 version of the runtime.

In this case, the user may install the default Mono SDK packages when
asked by the configure script, which only includes the 4.0 compiler by
default (dmcs). At that point, banshee can already be compiled, but
the configure script would insist in requiring a 2.0 compiler. If the
user installs it, compiles Banshee and launches the "run" target, she
may get a runtime exception because of a runtime version mismatch, like
in bgo#675113.

This problem is commonly known, and there is a clear workaround for it:
http://orangesquash.org.uk/~laney/blog/posts/2011/10/mono-gotcha/
However it poses a small barrier of entry for new developers that try
to compile and run banshee from sources for the first time.

Now the configure script is smarter and tries to guess harder if there
is a C# compiler, even one that targets a higher version of the runtime
than the one that is required to compile banshee.

This possibility is only enabled in case the Mono version found is 2.8
or higher, because Mono 2.6.1 included the 4.0 profile only as a
"preview" [1] and might not be stable enough.

[1] http://www.mono-project.com/Release_Notes_Mono_2.6.4#C.23_Language

(commit taken from Banshee 3d3f7899465ee46e634b53c236401f612dac1492)
[Build] Automatically use dmcs if available by default
Merge branch 'stable'
[lib/agsxmpp] prevent service-unavailable iq loop with the server (closes: #889)
Merge pull request #118 from oli-obk/fix/service-unavailable-loop
[Frontend-GNOME] Initial treeview navigation implementation (closes: #107, #292)

This treeview based chat navigation replaces the tab based navigation.

Known issues:
 * Missing keyboard binding (uses tab navigation)
 * Missing context menu (to close)
 * Missing chat icons
 * Desktop notifications are always shown
 * Items are unsorted
 * Flickering when changing the selection
[Frontend-GNOME] Fixed showing activity/events of active chat if window is unfocused (closes: #879)
Merge branch 'stable'
[Frontend-GNOME] Use ChatViewManager as authoritative CurrentChatView source
Merge branch 'master' into experiments/treeview
[Frontend-GNOME] Alphabetically sort the chat tree
[Frontend-GNOME] Only show desktop notifications for invisible chat rows

Thanks goes to Carlos Martín Nieto for API hints
[lib/agsxmpp] agsxmpp now supports forced tls
[Engine-XMPP] force tls if encryption is enabled, try tls otherwise
Merge pull request #120 from oli-obk/feature/use_encryption
Merge branch 'stable'

Conflicts:
	lib/agsxmpp
[Frontend-GNOME] Support icons in chat tree
[Frontend-GNOME] Avoid re-rendering the chat in the tree too often
[Frontend-GNOME] Removed unneeded remoting call from Notebook.OnSwitchPage()