* Completed property hooks, so that the underlying Ant1 project
  is not used for setting, getting or resolving properties.

* Made PropertyResolver.resolveProperties()take a TaskContext,
  instead of Avalon Context. (We can always split out a generic
  interface later, if need be.) Ant1 compatibility layer user
  ClassicPropertyResolver, which needs a better name.

* Added modified BuildException, which incudes a Myrmidon-friendly
  getCause() method, to allow Ant1 exceptions to be properly cascaded.

* DefaultTaskContext:
    - Allow "+" in property names.
    - Implemented DefaultTaskContext.getProperties()
    - No longer implements avalon Context (not needed)


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@271924 13f79535-47bb-0310-9956-ffa450edef68