Touch up the comments in the 'tag-contains' branch

Thomas Braun pointed out several documentation shortcomings.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

builtin/tag.c

@@ -99,12 +99,11 @@ static int contains_test(struct commit *candidate,
 }
 
 /*
- * This stack on the heap mimics the real stack in the previous implementation
- * of contains_recurse() that had to be replaced because it easily led to a
- * stack overflow.
+ * Mimicking the real stack, this stack lives on the heap, avoiding stack
+ * overflows.
  *
- * Every stack item points at a certain commit whose parents are iterated over.
- * Each item's current parent is the current next stack item's commit.
+ * At each recursion step, the stack items points to the commits whose
+ * ancestors are to be inspected.
  */
 struct stack {
 	int nr, alloc;

t/t7004-tag.sh

@@ -1380,9 +1380,8 @@ test_expect_success 'multiple --points-at are OR-ed together' '
 	test_cmp expect actual
 '
 
-# what about a deep repo ?
-
 >expect
+# ulimit is a bash builtin; we can rely on that in MinGW, but nowhere else
 test_expect_success MINGW '--contains works in a deep repo' '
 	ulimit -s 64
 	i=1 &&