Re: [PATCH] git gui: Use git diff --submodule when available

Changed the use of submodule summary to diff --submodule because the
implementation in C is much faster than the submodule script. Also a test
has been added to make sure that the underlying git supports the diff
option --submodule (which was introduced in 1.6.6).

Signed-off-by: Jens Lehmann <redacted>
---

@@ -296,16 +304,6 @@ proc start_show_diff {cont_info {add_opts {}}} {
 		lappend cmd $path
 	}

-	if {[string match {160000 *} [lindex $s 2]]
-        || [string match {160000 *} [lindex $s 3]]} {
-		set is_submodule_diff 1
-		if {$w eq $ui_index} {
-			set cmd [list submodule summary --cached -- $path]
-		} else {
-			set cmd [list submodule summary --files -- $path]
-		}
-	}
-