[sdo] Updates to keys

[Frank Budinsky <frankb@ca.ibm.com>]

Hi Guys,
While reviewing the key sections (4.6 and 8.2) in the latest draft from 
Ron, I was thinking that it's quite ugly that key and keyType are open 
content properties given that key is only ever used on Property, and 
keyType only on Type? The fact that we also need sdox: annotations (open 
content properites), makes it seem even more strange. It would seem to be 
a lot cleaner to just make them defined properties of the corresponding 
types, that is:

Section 5.1 - add this entry 
keyType |  9 | getKeyType()

Section 5.2 - add this entry
key     | 10 | isKey()
I ran it by Ron already, and he seems to agree. Unless anyone else has an 
objection, I will take a pass at reworking the spec update to describe 
them as defined properties.
Thanks,
Frank