implemented filter-branch for key info

Not tested yet but should work.

Noted a possible optimisation, which should probably be added, to
speed it up in cases where there is no uuid filtering being done.
It would need Annex.Branch to add a function like getRef that uses
catFileDetails, so the sha is also returned. The difficulty would be
making it support the precached file content; if it didn't it would
probably not be any faster and could even be slower. So probably the
precaching would need to be changed to also cache the sha.

Annex/Branch/Transitions.hs

@@ -7,7 +7,8 @@
 
 module Annex.Branch.Transitions (
 	FileTransition(..),
-	getTransitionCalculator
+	getTransitionCalculator,
+	filterBranch,
 ) where
 
 import Common