Merge branch 'vd/skip-cache-tree-update'

Avoid calling 'cache_tree_update()' when doing so would be redundant.

* vd/skip-cache-tree-update:
  rebase: use 'skip_cache_tree_update' option
  read-tree: use 'skip_cache_tree_update' option
  reset: use 'skip_cache_tree_update' option
  unpack-trees: add 'skip_cache_tree_update' option
  cache-tree: add perf test comparing update and prime

diff --cc Makefile
Simple merge

diff --cc sequencer.c
Simple merge

diff --cc t/helper/test-tool.c
Simple merge

diff --cc t/helper/test-tool.h
Simple merge