In compile(), reduce excess implicit reallocate-and-copy of stack.

If you use an array as a stack and don't make use of [assumeSafeAppend](http://dlang.org/phobos/object.html#assumeSafeAppend), then you'll get a bunch of excess reallocations and copying. See [this link](http://semitwist.com/articles/article/view/don-t-use-arrays-as-stacks) for a deeper explanation.