RFR (S) 8019417: JSR 292 javadoc should clarify method handle arity limits

[John Rose]

Please review this change for a change to the JSR 292 implementation:

http://cr.openjdk.java.net/~jrose/8019417/webrev.00

The change is to javadoc and unit tests, documenting and testing some corner cases of JSR 292 APIs.

Since the RI is already correct, there are no implementation code changes.

Thanks,
— John