Detect code-changes in FastTags and JavaExtentions

[mbknor]

Almost all code changes works as it should: changed templates and changed app code.

But when using GTFastTag or JavaExtentions there is a problem with changes.

The special-case here is that the template code is calling back into the app code.

Since this is currently done using a fixed classloader, we still see the old verison of the class, even though play2 has been "restarted" and is now using a new classloader.

This must be fixed.. But must prevent recompilation of the templates