DiskDevice API v2.3

Here's v2.3 of the DiskDevice API proposal. I hope and believe it 
contains all the changes we discussed, but I may have overlooked 
something in the flood of early April emails we had. :-)

http://www.dauwalder.net/DiskDeviceAPI_v2.3.zip

Here are a couple of notes/questions:

- For indicating whether a partition supports a given operation while 
still mounted, do you prefer "bool *whileMounted" or "bool 
*requiresUnmounting"? I've used the former because it's easier to 
type. :-)

- I left the parameters parameter in ValidateCreateChild() in case 
the child parameters somehow affect the min/max size of the potential 
child.

-	int32 CommitModifications(bool synchronously = true,
		BMessenger progressMessenger = BMessenger(),
		bool receiveCompleteProgressUpdates = true,
		BMessage *template = NULL);
still exists in BDiskDevice. We kind of talked about this previously, 
but I was never really convinced we came to a decision. I'm only kind 
of comfortable moving it into BPartition. Opinions?

- I haven't done anything about BPartitionableSpace vs. 
BPartitioningInfo, as that's still on the table. 

-Tyler