Merge branch 'jc/commit-hook-authorship' into maint

"git commit --author=$name" did not tell the name that was being
recorded in the resulting commit to hooks, even though it does do so
when the end user overrode the authorship via the "GIT_AUTHOR_NAME"
environment variable.

* jc/commit-hook-authorship:
commit: pass author/committer info to hooks
t7503: does pre-commit-hook learn authorship?
ident.c: add split_ident_line() to parse formatted ident line

diff --cc builtin/commit.c
Simple merge

diff --cc cache.h
Simple merge