Merge branch 'cc/trailers-corner-case-fix' into maint

The "interpret-trailers" helper mistook a multi-paragraph title of
a commit log message with a colon in it as the end of the trailer
block.

* cc/trailers-corner-case-fix:
  trailer: support multiline title
  trailer: retitle a test and correct an in-comment message
  trailer: ignore first line of message

diff --cc t/t7513-interpret-trailers.sh
Simple merge

diff --cc trailer.c
Simple merge