Fix http://issues.apache.org/bugzilla/show_bug.cgi?id=56283
Add support for running Tomcat 6 with ecj-P20140317-1600.jar (as drop-in replacement for ecj-4.3.1.jar).
Add support for value "1.8" for the compilerSourceVM and compilerTargetVM options.
Note that ecj-P20140317-1600.jar can only be used when running with Java 6 or later. The "1.8" options make sense only when running with Java 8 (or later).

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc6.0.x/trunk@1585997 13f79535-47bb-0310-9956-ffa450edef68