include empty directories when cleaning test-build

Files:
modified: /trunk/seam-gen/build-scripts/build.xml (try)
modified: /trunk/seam-gen/icefaces/build-scripts/build.xml (try)
modified: /trunk/seam-gen/build-scripts/build-war.xml (try)
modified: /trunk/seam-gen/icefaces/build-scripts/build-war.xml (try)