Improve array interop test so it covers taking a class reference to an array.
Check we can call clone() on native arrays.
Issue #882: Static optimization of "for (x in intArray.interable) {}" (and other native array cases).

Issue #882: Also in cases where we have an indexable thing
(Array, native array or ArraySequence) let's support having a step size:
"for (x in indexableTing.by(step)) {}"
Optimization: Fix tests
Improve tests for native array iteration optimization
Enable the optimization tests now they're mostly fixed.
Issue #882 (and #1467): Add an optimization for "for (i in start:length) { ... }" and "for (i in (start:length).by(step)) { ... } where start is Integer or Character
Issue #882 (and #1467): Tests for the optimization for "for (i in start:length) { ... }" and "for (i in (start:length).by(step)) { ... } where start is Integer or Character
Issue #882 (and #1467): Update existing tests change by the optimization for "for (i in start:length) { ... }" and "for (i in (start:length).by(step)) { ... } where start is Integer or Character