git-format-patch: make --binary on by default

It does not make much sense to generate a patch that cannot be
applied.  If --text is specified on the command line it still
takes precedence.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

builtin-log.c

@@ -470,6 +470,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	if (!rev.diffopt.output_format)
 		rev.diffopt.output_format = DIFF_FORMAT_DIFFSTAT | DIFF_FORMAT_SUMMARY | DIFF_FORMAT_PATCH;
 
+	if (!rev.diffopt.text)
+		rev.diffopt.binary = 1;
+
 	if (!output_directory)
 		output_directory = prefix;