Tomcat 6 support

[blabno]

Why is startInternal used instead of start?
First one is present since 7.x.

https://github.com/HotswapProjects/HotswapAgent/blob/master/TomcatPlugin/src/main/java/org/hotswap/agent/plugin/tomcat/TomcatPlugin.java#L90

[edudant]

Start method public final synchronized void start() throws LifecycleException is defined in LifecycleBase, common for all beans created from it and is final. Plugin needs access to WebappLoader private variables - especially to get classLoader.

It should be possible to check if the method startInternal exists and do some kind of fallback for older versions.

[edudant]

Tomcat is now fully supported. See https://github.com/HotswapProjects/HotswapAgentExamples/blob/master/plain-servlet/run-tests.sh for supported versions.