ObjectColumnSelector/JS aggregator support for multi-valued columns.

~~You may notice that one of the tests detects the array by using ```typeof a !== 'string'``` instead of ```Arrays.isArray(a)``` or ```typeof a === 'array'```. This is because the latter two methods don't work. The type of "a" is actually "object" even though it behaves like an array (subscripting and indexOf both work). I don't know why...~~

Xavier found out that Context.newArray makes better arrays than Context.javaToJS, so this does that now.

PS, the ```cx.getWrapFactory().setJavaPrimitiveWrap(false)``` business causes the strings inside the array to get treated as actual JS strings. Otherwise they get treated as wrapped Java objects and you can't actually compare them to real JS strings.