changed xs:ID to xs:string in all schemas

[Matt Jones]

As we discussed earlier today, the use of xs:ID as the type for our id 
elements has prevented us from using completely numeric values in the id 
elements.  Thus, we decide to change from xs:ID to xs:string in all of 
these cases.  I have now implemented this, and tested validation against 
the instance documents we were using yesterday.  Validation now allows 
values like "1234".  This takes care fo the sixth action item from our 
conference call today.

I also fixed a syntax error from my earlier checkin today that I 
discovered while testing validation.

Cheers,

Matt