mdiff: distinguish diff headers from hunks in unidiff() Let unidiff return the list of headers it produces (lines '--- <original>' and '+++ <new>') apart from diff hunks. In patch.diff(), we combine headers generated there (not specific to unified format) with those from unidiff(). By returning a list of header lines, we do not append new lines in datetag inner function of unidiff() so that all header lines are '\n'.join-ed in a similar way.