Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=55893
Split AccessLogValve and extract the formatting logic in an AbstractAccessLogValve to facilitate other implementations that output to destinations other than files.
Patch provided by Cyrille Le Clerc

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1557113 13f79535-47bb-0310-9956-ffa450edef68
More graceful handling (a 403 rather than a 500 response) when file permissions allow Tomcat to know a resource exists but not to read it

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1557127 13f79535-47bb-0310-9956-ffa450edef68