[ISSUE-22] Provenance Revision Agent

Hi all,
Please find attached a revised proposal for the translation revision 
agent provenance data category. Based on the feedback form the previous 
call for concensus 
(http://lists.w3.org/Archives/Public/public-multilingualweb-lt/2012Jul/0256.html) 
and discussions with David I've made the following changes:

- included the pointer and refPointer variants consistent with other 
data categories
- to split the the global rule between transation agent proveance and 
translation revision provence, I ended up actually splitting this into 
two data categories. This post contains the translation_revision_ agent 
provenance. I'll send on the other, the translation agent provenance 
shorlty, though this will follow the same pattern
- I allow only one value rather than multiple ones for each type of 
agent and explicitly include attribute so the three types can be 
differentiated - so the data types can be interpreted unambiguously
- slimmed down the description

comments welcome. One open question is whether the naming of 
'translationRevision' (or 'transRev') could be better named 'postedit' 
(or 'pe')?

cheers,

Dave