completion: learn about --man-path

Signed-off-by: John Keeping <john@keeping.me.uk>
Acked-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -2513,6 +2513,7 @@ __git_main ()
 			--exec-path
 			--exec-path=
 			--html-path
+			--man-path
 			--info-path
 			--work-tree=
 			--namespace=

t/t9902-completion.sh

@@ -231,6 +231,7 @@ test_expect_success 'double dash "git" itself' '
 	--exec-path Z
 	--exec-path=
 	--html-path Z
+	--man-path Z
 	--info-path Z
 	--work-tree=
 	--namespace=