Rule proposal: warn against unused array iterator method return values

There are some function calls where the return value should not be ignored (like some, indexOf, concat, map, etc.) or the function call doesn't make sense. Would be nice to cover this with the no-unused-expressions lint. I did test the snippets below on current master, they both don't fail.

function foo(arr) {
  if (arr) {
    arr.some(el == 'myval'); // should be: return arr.some(el == 'myval');
  }
  return undefined;
}

function foo(arr) {
  var merged = arr.reduce(function (a, b) {
    a.concat(b);  // should be: return a.concat(b);
  });
}