Show binary file size change in diff --stat

Show binary file size change in diff --stat

Previously, a binary file in the diffstat would show as:

 some-binary-file.bin       |  Bin

The space after the "Bin" was never used.  This patch changes binary
lines in the diffstat to be:

 some-binary-file.bin       |  Bin 12345 -> 123456 bytes

The very nice "->" notation was suggested by Johannes Schindelin, and
shows the before and after sizes more clearly than "+" and "-" would.
If a size is 0 it's not shown (although it would probably be better to
treat no-file differently from zero-byte-file).

The user can see what changed in the binary file, and how big the new
file is.  This is in keeping with the information in the rest of the
diffstat.

The diffstat_t members "added" and "deleted" were unused when the file
was binary, so this patch loads them with the file sizes in
builtin_diffstat().  These figures are then read in show_stats() when
the file is marked binary.

Signed-off-by: Andy Parkins <andyparkins@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>