Merge branch 'jk/pretty-subject-cleanup'

Merge branch 'jk/pretty-subject-cleanup'

Code clean-up in the "git log" machinery that implements custom log
message formatting.

* jk/pretty-subject-cleanup:
  format-patch: fix leak of empty header string
  format-patch: simplify after-subject MIME header handling
  format-patch: return an allocated string from log_write_email_headers()
  log: do not set up extra_headers for non-email formats
  pretty: drop print_email_subject flag
  pretty: split oneline and email subject printing
  shortlog: stop setting pp.print_email_subject