Using() modifier missing on NUnit.Framework.Contains.Item()

There is a Using() modifier on NUnit.Framework.Is.EqualTo() (I'm using v2.5.8,) but I'd like to have one on NUnit.Framework.Contains.Item(), too. Here's what you'd have to do.

Make CollectionItemsEqualConstraint.comparer protected:
< public abstract class CollectionItemsEqualConstraint : CollectionConstraint
< {
< private NUnitEqualityComparer comparer = NUnitEqualityComparer.Default;
-------
> public abstract class CollectionItemsEqualConstraint : CollectionConstraint
> {
> protected NUnitEqualityComparer comparer = NUnitEqualityComparer.Default;

Add the Using modifier to CollectionContainsConstraint:
> /// <summary>
> /// Flag the constraint to use the supplied Comparison object.
> /// </summary>
> /// <param name="comparer">The Comparison<T> object to use.</param>
> /// <returns>Self.</returns>
> public CollectionContainsConstraint Using<T>(Comparison<T> comparer)
> {
> this.comparer.ExternalComparer = EqualityAdapter.For(comparer);
> return this;
> }

Variants go similar.

Narrow the return type of Contains.Item() so the new modifier becomes accessible:
> /// <summary>
> /// Creates a new CollectionContainsConstraint.
> /// </summary>
> /// <param name="item">The item that should be found.</param>
> /// <returns>A new CollectionContainsConstraint</returns>
> public static CollectionContainsConstraint Item(object item)
> {
> return new CollectionContainsConstraint(item);
> }

Call the supplied comparer at the appropriate time. I suggest that this should be first after comparing for null and reference equality, since it is an explicit override in the test code:
> public bool ObjectsEqual(object x, object y)
> {
...
> if (object.ReferenceEquals(x, y))
> return true;
>
> if (externalComparer != null)
> return externalComparer.ObjectsEqual(x, y);
>
> Type xType = x.GetType();
> Type yType = y.GetType();
>
> if (xType.IsArray && yType.IsArray && !compareAsCollection)
> return ArraysEqual((Array)x, (Array)y);