Change RevWalkTestCase to use RevCommit, not ObjectId
We build a RevWalk once per test, and only execute a single traversal
in that test run. Its more clear to use the RevCommit type from that
object pool to represent a commit entity than the generic ObjectId.
When creating a new commit we allocate its RevCommit from the pool,
but we delay parsing until as late as necessary. This is needed for
at least one test where it validates whether or not the parents of a
commit were allocated after traversal finishes.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>