p/69640134 b/14272061 Low-hanging client side speedups; throttle instead of debounce on refresh, only fake-AJAX Mustaches once, and prerender Mustaches in the background.
Fix for throttle() change in Cacheable refresh deleting _pending_refresh before returning its deferred
Fixups and add comments

* Partially revert changes to ajaxTransport used for Mustache template
  loading
* Fix parameter order in $.throttle and move deletion of
  `this._pending_refresh` to after completion of the Ajax call
Don't throttle `refresh()` triggered by `refresh()` callback

* Previously, if a callback on a `refresh()` deferred triggered another
  refresh, it would have been throttled.
Merge pull request #1277 from reciprocity/feature/basic-client-speedups

Easy client-side speedups