completion: add dirstat and friends to diff options

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index daccbcc..88b1b3c 100755
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -927,6 +927,8 @@
 			--inter-hunk-context=
 			--patience
 			--raw
+			--dirstat --dirstat= --dirstat-by-file
+			--dirstat-by-file= --cumulative
 "
 
 _git_diff ()