Fixed issue #147

Looks like this fixes the issue. But only on TomEE. The problem was that `externalContext.encodeActionURL()` was called with the context-relative URL and not with the absolute URL (including the context path). In this case Tomcat didn't add the jsessionid.

I'm still having problems with my test on AS7. Not sure why. Looks like AS7 _never_ adds any jsessionid. Not sure why. There is no web.xml in the test archive which disables this.

I'll create this pull request to check my change against the other containers.