RFR 8053910: ScriptObjectMirror causing havoc with Invocation interface

[A. Sundararajan]

Please review http://cr.openjdk.java.net/~sundar/8053910/

ScriptObjectMirror, wrap/unwrap has caused pain. Uniformly wrapping all 
ScriptObject instances to be ScriptObjectMirror whenever Java boundary 
is crossed. Hopefully, it'll be easier to understand and code around 
ScriptObjectMirrors in Java side.

Thanks
-Sundar