* Use multi-parent ClassLoaders for antlibs and extensions, so that each
  extension jar is loaded by a single ClassLoader in the hierarchy.  Allows
  classes from extensions to be shared across dependent antlibs and extensions.

* Changed contract of ClassLoaderManager.createClassLoader( File[] ), so that
  it creates a new ClassLoader each time it is called.

* Changed ExtensionManager, so that it no longer extends PackageRepository.

* Added a few test cases for DefaultClassLoaderManager.

* Moved responsibility for checking myrmidon.home and building the various paths,
  from DefaultEmbeddor and DefaultExtensionManager to EmbeddedAnt.  Use the
  platform path separator for the paths, rather than the | char.

* Use EmbeddedAnt in AbstractProjectTest, rather than using an Embeddor directly.

* AbstractComponentTest was not parameterising or initialising the test
  components.


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@272180 13f79535-47bb-0310-9956-ffa450edef68