6759414: javascript engine can not write to StringWriter
6869617: RhinoScriptEngine bug : ScriptException cause not set (with fix)
7012701: Add a test to check that Rhino's RegExp parser accepts unescaped '['
Reviewed-by: alanb, jjh
Updating Rhino javascript engine with version 1.7R3. Issue 6427783 (E4X support is missing from Sun's Mozilla JavaScript implementation) is also fixed as a side-effect.
Reviewed-by: alanb, jjh