Use Stream.prototype._label for Handlebars compat makeBoundHelper.
Set Stream._label in constructor.
Merge pull request #9756 from rwjblue/update-compat-make-bound-helper-to-stream-label

Use Stream.prototype._label for Handlebars compat makeBoundHelper.
Merge pull request #9757 from rwjblue/set-stream-label-in-init

Set Stream._label in constructor.
Use Stream.prototype._label for HTMLBars {{unbound}} helper.
Merge pull request #9758 from rwjblue/htmlbars-make-unbound-use-label

Use Stream.prototype._label for HTMLBars {{unbound}} helper.
HTMLBars compiler plugin for {{each .. in ..}}
HTMLBars compiler plugin for {{with .. as ..}}