XMLUnit.NET 2.9.0

This release fixes a bug for a very specific setup and makes ISource disposable.

Full details:

• ISource now extends IDisposable to allow releasing unmanaged resources used when building sources from files or URIs.

  This change is backwards incompatible if you are providing ISource implementations of your own.
  #33.

• DefaultNodeMatcher with multiple ElementSelectors could fail to find the best matches as the order of ElementSelectors should select them.
  Issue similar to xmlunit/#197