Bug#295298: gksu error reporting could be more friendly

[Sebastien Bacher]

Package: gksu

This bug has been opened here: https://bugzilla.ubuntu.com/2498

"Select "Root Terminal" in the GNOME menu.
Type an incorrect password in the gksudo dialog.

The displayed error message reads:
"Failed to run /usr/bin/x-terminal-emulator as user root:
 Child terminated with 1 status"

It should explain that the cause of the error is an incorrect password instead
of some internal error in x-terminal-emulator:
"Failed to run /usr/bin/x-terminal-emulator as user root:
 Incorrect password"

If possible, there should be a specific error message for the "Root Terminal"
because root has no password of itself by default:
"Failed to run a root terminal: incorrect password""