Would be helpful for tests to test br inside try-catch

[keithw]

The current tests do not test br* instructions inside a try-catch block (either inside the body of the try block or one of the catch blocks). There are some subtleties here that I suspect it would be easy for an implementation to screw up without test coverage. (E.g., br out of a try block body to somewhere that then throws an exception -- the stack should be unwound to the correct place.) It would be helpful to have test coverage for these scenarios.