Did most of the optimisations that recent profiling suggested. 
This sped up a `git annex find` from 3.53 seconds to 1.73 seconds.
And, `git annex find --not --in remote` from 12.41 seconds to 5.24 seconds.
One of the optimisations sped up git-annex branch querying by up to 50%,
which should also speed up use of some preferred content expressions.
All in all, a very nice little optimisation pass.
