Merge branch 'rs/log-invert-grep-with-headers'

Merge branch 'rs/log-invert-grep-with-headers'

"git log --invert-grep --author=<name>" used to exclude commits
written by the given author, but now "--invert-grep" only affects
the matches made by the "--grep=<pattern>" option.

* rs/log-invert-grep-with-headers:
  log: let --invert-grep only invert --grep