Support extra diff information for binary files

[ColMelvin]

Since SVN 1.7, some changes to binary files have extra information in the diff. Specifically, after noting that the file is a binary type, it displays a second, empty diff for the (same) file -- one without hunks -- but with the filename and revision numbers.

Index: file
===================================================================
--- file        (revision 0)
+++ file        (revision 2)

Since this doesn't happen all of the time with binary files, it probably signifies something else. I'm not sure what though.

[ColMelvin]

This may be a header for the property diffs; investigation required.