GWTShell must not link public and autogenerated artifacts into the shell generated resource directory.

A generated selection script from a previous dev run could be served instead of a compiled selection script from the "out" directory.

Found by: bobv
Review by: jat

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7037 8db76d5a-ed1c-0410-87a9-c151d255dfc7