Make EShell a subclass of UniqueApp and handle single-instance negotiation.
When another Evolution process is running:
- Running "evolution" will simply present the existing windows.
- Running "evolution -c <view>" will open a shell window set to <view>.
- Running "evolution <uri>" will open an appropriate window for <uri>.
The second process will then terminate immediately.
svn path=/branches/kill-bonobo/; revision=37147