Use forked version of slf4j to fix concurrency issue with static binding

The slf4j-api static binding is not thread safe. A fork of slf4j-api was needed for EAP so we might as well patch WildFly too. The slf4j bugzilla is http://bugzilla.slf4j.org/show_bug.cgi?id=176. The patch used in the fork is attached to the bz.