Fixes to Expsenses sample pom.xml

- Upgraded to latest GAE so that GPE can use a currently-shipping GAE SDK version
- Downgraded Datanucleus Enhancer for GAE compatibility
- Explicit Xalan dependency
- Other sundry fixes

Review at http://gwt-code-reviews.appspot.com/1007801

Review by: drfibonacci@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9078 8db76d5a-ed1c-0410-87a9-c151d255dfc7