fix #1074 Fixed error with yeild in ComputedPropertyName

[tuchida]

Closes #1074

Running the following code in non-interpreted mode will throw NullPointerException. ref. #1074 (comment)

function* g() {
  var obj = {
    get [yield]() { return 'get yield'; }
  };
}

Test262SuiteTest does not display the exception, but you can see it by uncommenting this line.

rhino/tests/src/test/java/org/mozilla/javascript/tests/Test262SuiteTest.java

Lines 635 to 638 in cc302b4

	// enable line below to print out stacktraces of unexpected exceptions
	// disabled for now because too many exceptions are throw
	// Unexpected non-Rhino-Exception here, so print the exception so it stands out
	// ex.printStackTrace();

There are many exceptions other than NullPointerException, so I will leave the comment as they are. For example, java.lang.RuntimeException: Failed to build a scope with the harness files. errors seems to be resolved by #1540.

[tuchida]

The properties are a mixture of String, Integer and Node, where Node is Computed Property Name.

[gbrail]

Good progress and thanks! Can you please re-base this on top of the latest to pick up the new test262 changes? Thanks!

[gbrail]

Thanks for fixing this -- looks good!