Updated common.ant.xml to copy pom.xml (if found) to  build/out
Added .place-holder to ensure war dir existence

Review at http://gwt-code-reviews.appspot.com/782801

Review by: rice@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@8602 8db76d5a-ed1c-0410-87a9-c151d255dfc7