Merge branch 'jc/merge-bases'

The get_merge_bases*() API was easy to misuse by careless
copy&paste coders, leaving object flags tainted in the commits that
needed to be traversed.

* jc/merge-bases:
get_merge_bases(): always clean-up object flags
bisect: clean flags after checking merge bases

diff --cc bisect.c
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc builtin/rev-parse.c
Simple merge

diff --cc commit.c
Simple merge

diff --cc commit.h
Simple merge

diff --cc merge-recursive.c
Simple merge

diff --cc notes-merge.c
Simple merge

diff --cc revision.c
Simple merge

diff --cc sha1_name.c
Simple merge

diff --cc submodule.c
Simple merge