diff: add option to report binary files in raw diffs

When generating patch diff output, if either side of a filepair is detected as binary, Git omits the diff content and instead prints a "Binary files differ" message. From this message it is known that at least one of the files in the pair is considered binary, but not exactly which ones.

Add a --report-binary-files diff option that, when enabled, extends the raw diff output format to explicitly indicate for each file whether is was considered binary or not.

Signed-off-by: Justin Tobler jltobler@gmail.com

Related: #566