Reduce the visibility of the exception generated if a browser abort a download

A user can cancel a download, the browser can only download a chunk of a video to know what it is...

2013-09-07 07:13:53,574 [ajp-apr-8009-exec-7] ERROR ServletUtil - OLAT::ERROR ^% N9-E13 ^% org.olat.core.gui.media
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0 ^% client browser probably abort when serving media resource ^%
>>>stack of 1.cause::org.apache.catalina.connector.ClientAbortException: null
-> at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:406)
at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:480)
at org.apache.tomcat.util.buf.ByteChunk.append(ByteChunk.java:366)
at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:431)
at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:419)
at org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:91)
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1793)
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1769)
at org.apache.commons.io.IOUtils.copy(IOUtils.java:1744)
at org.olat.core.gui.media.ServletUtil.serveFullResource(ServletUtil.java:198)
at org.olat.core.gui.media.ServletUtil.serveResource(ServletUtil.java:105)
>>>stack of 2.cause::java.io.IOException: Failed to send AJP message ->
at org.apache.coyote.ajp.AjpAprProcessor.output(AjpAprProcessor.java:294)
at org.apache.coyote.ajp.AbstractAjpProcessor$SocketOutputBuffer.doWrite(AbstractAjpProcessor.java:1124)
at org.apache.coyote.Response.doWrite(Response.java:505)
at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:401)
at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:480)
at org.apache.tomcat.util.buf.ByteChunk.append(ByteChunk.java:366)
at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:431)
at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:419)
at org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:91)
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1793)
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1769)