Fixed call to varargs JS method without any arg.
Made methods of j.l.Object work on JSAny values.

This means that yes, pure JavaScript values can be stored
in a variable of type j.l.Object (aka Any or AnyRef after
erasure), without boxing, and everything is going to be fine.
java.lang.String is now compiled down to primitive JS string.

Following suit to JSAny values, such string values can be
stored in variables of type j.l.Object without being boxed,
and yet all methods, type tests, etc. will continue to work
just fine.