[UCR] Requirements' list updated for UC2

Hi,

I've updated the list of requirements motivated by UC2 [1] as discussed 
during the F2F meeting in Athens:
1. the new list of requirements [2] for RIF has been considered for the 
motivates links of the use case;
2. the requirements marked as general in [2] have been deleted from the 
motivates links;
3. a more detailed discussion of the coverage discriminators [3] has 
been added.

For preparing the next version of the UCR document, the authors of the 
use cases found in [4] should also update the requirements' list 
according to the three points listed above.

Best regards from Munich,
Paula

[1] 
http://www.w3.org/2005/rules/wg/wiki/UCR/Negotiating_eCommerce_Transactions_Through_Disclosure_of_Buyer_and_Seller_Policies_and_Preferences
[2] http://www.w3.org/2005/rules/wg/wiki/UCR/Requirements
[3] http://www.w3.org/2005/rules/wg/wiki/Rulesystem_Arrangement_Framework
[4] http://www.w3.org/2005/rules/wg/wiki/UCR