Merge branch 'wh/author-committer-ident-config'

Four new configuration variables {author,committer}.{name,email}
have been introduced to override user.{name,email} in more specific
cases.

* wh/author-committer-ident-config:
config: allow giving separate author and committer idents

diff --cc blame.c
Simple merge

diff --cc builtin/am.c
Simple merge

diff --cc builtin/commit.c
Simple merge

diff --cc cache.h
Simple merge

diff --cc config.c
Simple merge

diff --cc log-tree.c
Simple merge

diff --cc sequencer.c
Simple merge