The walk package contains walk.Some() and walk.All() which let you
walk the Chunk graph starting at a given Ref.
I also added GetReachabilitySetDiff(), which will determine which
refs in a given ChunkSource can be reached from one given ref, but not
the other.
Towards issue #82
It turns out these functions aren't actually generally useful,
because they deal in Values and Refs, while what we actually
want is to deal in chunks. So...
Revert "Settle big/small vs to/from ONCE AND FOR ALL"
This reverts commit f51c575cd2.
Revert "Add a naive Diff() function between two Values."
This reverts commit 662bc5e3c4.
Given two refs, we need to be able to determine the set of chunks
reachable from one that cannot be reached from the other. This patch
adds a naive implementation of this functionality that essentially walks
the value tree down from the values pointed to by two refs and compares them.
It also has a little command-line driver, but this may be removed.
Fixes issue #82
Aaron Boodman