Do you really need to set the default handler? Generally, Mac
applications merely advertise that they are capable of handling a
given URL scheme and it's left to the user to pick the default
handler. To merely advertise the capability, see the documentation
of the CFBundleURLTypes key of the Info.plist file:
That's the best way to do it. However, some programs tend to override
the user's choices for default URL handlers. I've noticed that the
Finder, for example, is very adamant about making itself the default
FTP URL handler.
