Improve the resolution of the extension point to bind to:
- first try the extension point which might be in the same file
- then try the one in the root file

Still some work to do: there might be intermediate file in the import stack which we would to resolve the name against, but the ProjectHelper doesn't hold the prefix stacking.



git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@1373326 13f79535-47bb-0310-9956-ffa450edef68