* generator/Signal.cs : add try/catch blocks to native callback
delegates so that exceptions are not propagated across the native
boundary. Now raises GLib.ExceptionManager.UnhandledException.
* glib/ExceptionManager.cs : new class with UnhandledException
event and a static method to raise it.
* glib/Signal.cs : wrap the generic EventHandler callback delegate
with try/catch blocks and raise the UnhandledException event.
svn path=/trunk/gtk-sharp/; revision=73840
