Add support for a group property in LogFilePatternReceiver in order to allow logs from multiple cluster nodes to be combined in a single table by using GROUP as the event routing, and add support for the 'chainsaw' group for chainsaw-generated logs.  Also updated the valid characters in the filereceiver timestampformat for java 7.

git-svn-id: https://svn.apache.org/repos/asf/logging/chainsaw/trunk@1593840 13f79535-47bb-0310-9956-ffa450edef68