[RFC/PATCH 4/4] rev-cache: tentative integration into rev-list + tests

This patch introduces a tentative step towards integrating rev-cache into the internal revision walker.  Cache traversal is added to both limited and unlimited revision walks, and FACE_VALUEd objects are handled in list-objects.  Furthermore the unique object_list field is added to commit objects, to allow runtime association with a commit's cached 'unique' object list.

The traversal mechanism in rev-cache is updated to reflect the limiting methods used in rev-list.  Tests for coagulation and index generation are included, in addition to several verifying the correctness of integration.

Signed-off-by: Nick Edelen <redacted>

---
 builtin-rev-cache.c       |   44 +++++++-
 commit.c                  |    2 +-
 commit.h                  |    1 +
 list-objects.c            |   19 +++-
 rev-cache.c               |  299 +++++++++++++++++++++++++++++++++++++++------
 revision.c                |   91 +++++++++++---
 t/t6015-rev-cache-list.sh |  120 +++++++++++++++++--
 7 files changed, 505 insertions(+), 71 deletions(-)