[MERGE] Annotation updates

[Robert Collins]

Robert Collins has voted tweak.
Status is now: Conditionally approved
Comment:
I don't know that line introduced by two branches should be assigned to 
the merge; perhaps it should be assigned to both branches? That is, why 
do we say line->revision rather than line->[revisions] ?

I really don't like meaningless variables. Please give them proper 
names, or at least a comment saying what they are.

docstring in your frozenheadscache is wrong ( it claims to preserve the 
api)


For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C47CFC907.3080607%40arbash-meinel.com%3E