Bug 961821: jit-support for writes into TypedObject arrays.

As part of above, alpha-renamed IonBuilder::setElemTryTyped to
IonBuilder::setElemTryTypedArray to keep clear the current distinction
between TypedObject and TypedArray.

Drive-by fix: Reference to Bug 894105 in comment had off-by-one typo.
Bug 961821: jit-support for writes into TypedObject arrays (r=nmatsakis).

As part of above, alpha-renamed IonBuilder::setElemTryTyped to
IonBuilder::setElemTryTypedArray to keep clear the current distinction
between TypedObject and TypedArray.

Drive-by fix: Reference to Bug 894105 in comment had off-by-one typo.
Bug 961821: tests for jit-support for writes into TypedObject arrays (r=pnkfelix).

These iteration counts were selected to be close to the minimum number
necessary to expose bugs while working on this patch (see comments in
Bug 961821 for more details here).  Note that they are all 500
iterations (not 5000); please be wary of reducing the iteration count
further without first ensuring that the jit has time to compile this
code.