Merge branch 'ma/skip-writing-unchanged-index'

Internal API clean-up to allow write_locked_index() optionally skip
writing the in-core index when it is not modified.

* ma/skip-writing-unchanged-index:
  write_locked_index(): add flag to avoid writing unchanged index

diff --cc builtin/add.c
Simple merge

diff --cc builtin/commit.c
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc builtin/mv.c
Simple merge

diff --cc builtin/rm.c
Simple merge

diff --cc cache.h
Simple merge

diff --cc read-cache.c
Simple merge

diff --cc sequencer.c
Simple merge