Merge branch 'jk/combine-diff-binary-etc'

* jk/combine-diff-binary-etc:
  combine-diff: respect textconv attributes
  refactor get_textconv to not require diff_filespec
  combine-diff: handle binary files as binary
  combine-diff: calculate mode_differs earlier
  combine-diff: split header printing into its own function

diff --cc diff.c
Simple merge

diff --cc userdiff.c
Simple merge