Fix the pb of the loading of the BouncyCastle classes in JBoss 6.x

Add a servlet context listener to load external jarlib like the bouncy castle one. JBoss AS 6.x doesn't load properly such jarlib as they handle explicitly the classpath when registering themselves as a JCE provider. So, the classes in these jarlibs aren't accessible in the classpath of the webapp. To fix this behavior, the servlet context listener ExternalLibLoader first adds the libraries in the SILVERPEAS_HOME/repository/lib directory and then parses the property 'bypass.jboss.vfs' in the silverpeas configuration file general.properties and for each classes listed in the property, it loads them explicitly with the system classloader.