(ScriptEngine) Initialize default output and error writers
(PyScriptEngine) eval and evalFile do not have to throw exceptions
(PyScriptEngine) flush the error writer

... so that the exceptions are properly written
(ScriptEngine) Rename 'eval' to 'exec' since nothing is evaluated, strictly speaking

(I would expect 'eval' to return something)
(ScriptEngine) Rename 'evalFile' to 'execFile' since nothing is evaluated, strictly speaking

(I would expect 'eval' to return something)