[BUGFIX beta] contextualElements, handle omitted start tags

During a renderTree call, look to the morphs for information about the
contextualElement. Pass this to the Ember renderer, which in turn passes
it to the buffer for use when generating an element.

Here I've changed the morph creation points to explicitly pass a
contextualElement. This avoids the possibility of createMorph's fallback
to document.body happening.

Additionally, strip omitted start tags even if the child node causing
their generation is after a script tag. See the long comment in
`render_buffer`.
[BUGFIX beta] Whitespaces fixes and other IE8 issues resolved
[BUGFIX beta] Revert passing context a second time
[BUGFIX beta] Bump HTMLBars for IE8 fixes
[BUGFIX beta] Don't mutate context element during morph hydration
[BUGFIX beta] Fix bad test. Cannot nest p tags.
[BUGFIX beta] Fix another bad p tag test.
[BUGFIX beta] buffer tests to avoid string(), toLowerCase()