Hi,

-soundhw, -M, -cpu and -d options use the '?' to display the list of 
possibilities, whereas -clock uses 'help'. This has to be made consistent.

Some debug output is shown when -clock option is specified, which 
displays list of available clocks. In my opinion, interest is very 
limited (as invalid specified clocks are already printed, and list can 
be obtained with -help)

When no available clock has been specified, display the list of valid 
clock names and exit, instead of continuing with the default option 
(once again, to be consistent with other options of Qemu)

Attached patch fixes these 3 issues.

Hervé