Extend UnifiedVirtualFile API with no-check findChild methods

The UnifiedVirtualFile abstraction in quite used for accessing file/resources in deployments. Most of the time, though, the lookup of unified virtual file children leads to nothing (the required resource is simply missing) and a localized IOException is thrown. In most scenarios, that's not an actual "error", the procedure just implies trying multiple locations, and the exception is trapped and in most cases not even logged.
We need new flavors of findChild(String child) and getChildren() methods also accepting a boolean flag to suppress exception, log a message (if the log level is enabled) and return null / empty collection if nothing is found.
The new methods are to then to be used for instance to speed-up the jbossws-common ResourceResolverImpl, which currently badly affects performances in the jbossws-cxf stack, being is used whenever the Apache CXF resource resolver manager is also used.