gksu:

* better checking for what caused 'su' to fail
* support -c to specify command
* support different shell (-s on su)
* if command is not given, ask for it in the GUI (?)
   - call gksuexec

gksuexec:

* support more gksu command line options
   - login shell, preserv env
* support calling gksudo and its options
   - set home