RFR 8054651: Global.initConstructor and ScriptFunction.getPrototype(Object) can have stricter types

[A. Sundararajan]

Please review http://cr.openjdk.java.net/~sundar/8054651/

PS. also contains few minor javadoc fixes to get no errors with "ant 
javadoc" target as well as excluding a test262 test from test262 run 
(for which a bug has been filed already).

Thanks
-Sundar