Pick up dev/build.xml fix from branches/farewellSwt

svn merge --ignore-ancestry \
  https://google-web-toolkit.googlecode.com/svn/branches/farewellSwt -c6276 .



git-svn-id: https://google-web-toolkit.googlecode.com/svn/releases/2.0@6277 8db76d5a-ed1c-0410-87a9-c151d255dfc7