Failure to load beans.xml from multiple locations

URLScanner is depending on there being only one instance of META-INF/beans.xml on the classpath when loading beans.xml from jar. I don't have a standalone example of this, because it's occurring within eclipse, but in our case when scanning at startup the scanner would see beans.xml in the weld core jar but rather than loading it, would load two copies of a META-INF/beans.xml that it found on the classpath outside of that jar. Attached is a patch that fixes this for us.