attr: "binary" attribute should choose built-in "binary" merge driver

The built-in "binary" attribute macro expands to "-diff -text", so
that textual diff is not produced, and the contents will not go
through any CR/LF conversion ever.  During a merge, it should also
choose the "binary" low-level merge driver, but it didn't.

Make it expand to "-diff -merge -text".

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index a85b187..ead7254 100644
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -904,7 +904,7 @@
 macro attribute "binary" is equivalent to:
 
 ------------
-[attr]binary -diff -text
+[attr]binary -diff -merge -text
 ------------
 
 
diff --git a/attr.c b/attr.c
index 303751f..3f581b3 100644
--- a/attr.c
+++ b/attr.c
@@ -306,7 +306,7 @@
 }
 
 static const char *builtin_attr[] = {
-	"[attr]binary -diff -text",
+	"[attr]binary -diff -merge -text",
 	NULL,
 };
 
diff --git a/t/t6037-merge-ours-theirs.sh b/t/t6037-merge-ours-theirs.sh
index 8d05671..3889eca 100755
--- a/t/t6037-merge-ours-theirs.sh
+++ b/t/t6037-merge-ours-theirs.sh
@@ -54,7 +54,7 @@
 '
 
 test_expect_success 'binary file with -Xours/-Xtheirs' '
-	echo "file -merge" >.gitattributes &&
+	echo file binary >.gitattributes &&
 
 	git reset --hard master &&
 	git merge -s recursive -X theirs side &&