This was the last thing that was missing for complete support of all
function parameter declarations.
To ensure parameter lists stay valid a unit test was added that will
validate the argument lists and cause the test to fail if they cannot be
parsed.
This allows a script to create its own execution context so that it can
control when a coroutine is valid to play based on custom data.
Also adds a function which causes a coroutine to end in an error.
