Entries for directories are optional and mostly wasted space in most
archive formats (except as a place to hang ownership and filesystem
permissions), but "git archive" includes them. Follow suit.
This will make it easier in a later change to include empty
directories as placeholders for missing submodules.
Change-Id: I1810c686bcc9eb4d73498e4d3e763e18787b088a
Signed-off-by: Jonathan Nieder <jrn@google.com>
Matthias Sohn