Added new API to replace a SchemeHandler.


git-svn-id: http://sbuild.tototec.de/svn/sbuild/trunk@529 024a02f7-42f7-40fc-9f58-65666d1f2450
Added toString to TargetContextImpl.


git-svn-id: http://sbuild.tototec.de/svn/sbuild/trunk@530 024a02f7-42f7-40fc-9f58-65666d1f2450