Excluding classpath from jettyRunWar

I have a problem using slf4j-log4j12 with jettyRunWar plugin i get this output:

SLF4J: Class path contains multiple SLF4J bindings. SLF4J: Found binding in [jar:file:/C:/gradle-1.7/lib/logback-classic-1.0.9.jar!/ org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/E:/WorkingArea/www.spoilercup.com/spoilercup/ build/tmp/jettyRunWar/webapp/WEB-INF/lib/slf4j-log4j12-1.7.5.jar!/org/slf4j/impl /StaticLoggerBinder.class] SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.

SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory] log4j:WARN No appenders could be found for logger (CharacterController). log4j:WARN Please initialize the log4j system properly. log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more in fo.

How can I exclude this jar from jetty runtime ?

Thanks in advance.