Reduce the distribution size by sharing the libraries between the all and default configs

The lib directories of the 'all' and 'default' configuration currently differ only in 6 libraries:

avalon-framework.jar
hibernate-jbosscache2.jar
jacorb.jar
jbosscache-core.jar
jbosscache-pojo.jar
jgroups.jar

We can avoid the 17.7mb shared lib overhead by having a single copy of those libraries in a shared location, e.g.

JBOSS_HOME/server/lib

We would need a new jboss.shared.lib.url system property defaulting to ${jboss.server.base.url}/lib