Merge branch 'jt/use-trailer-api-in-commands'

Commands that operate on a log message and add lines to the trailer blocks, such as "format-patch -s", "cherry-pick (-x|-s)", and "commit -s", have been taught to use the logic of and share the code with "git interpret-trailer". * jt/use-trailer-api-in-commands: sequencer: use trailer's trailer layout trailer: have function to describe trailer layout trailer: avoid unnecessary splitting on lines commit: make ignore_non_trailer take buf/len trailer: be stricter in parsing separators