Stack frames in the ExceptionReport should have a fly-over window showing source code, where available

This would be very cool, move the mouse over the stack frame, have a popup window display an extract from the source (much like templates are displayed).

This requires that Tapestry be able to find the Java source. I'd say look in two places:
1) On the classpath
2) Under "src/main/java" in the current working directory (with the relative path configurable via a symbol).