Allow intents to be attached using an element

[ashok malhotra <ashok.malhotra@oracle.com>]

Today, intents are attached using the @requires attribute which allows 
no extensibility.
We argue that intents should also be attached using an element (at least 
as an option) so that
additional information can be provided.

In early versions of the policy spec we had 'strong' and 'weak' as 
qualifiers on the 'confidentiality' intent.
This has gone away but it may be useful to allow the user to add 
additional info to the intent, such as 'strong' and 'weak'
or even more specifically that a 128 bit encryption key be used.

Another usecase is to be able to turn an intent off and on using an 
attribute.  This is very useful during testing.

-- 
All the best, Ashok