Merge branch 'jc/maint-log-grep-all-match'

Merge branch 'jc/maint-log-grep-all-match'

Fix a long-standing bug in "git log --grep" when multiple "--grep"
are used together with "--all-match" and "--author" or "--committer".

* jc/maint-log-grep-all-match:
  t7810-grep: test --all-match with multiple --grep and --author options
  t7810-grep: test interaction of multiple --grep and --author options
  t7810-grep: test multiple --author with --all-match
  t7810-grep: test multiple --grep with and without --all-match
  t7810-grep: bring log --grep tests in common form
  grep.c: mark private file-scope symbols as static
  log: document use of multiple commit limiting options
  log --grep/--author: honor --all-match honored for multiple --grep patterns
  grep: show --debug output only once
  grep: teach --debug option to dump the parse tree