fix emberjs/website#1027 with unique header title
Merge pull request #3864 from mikepmunroe/master

fix emberjs/website#1027 with unique header title
Update header comment format to keep it on minify

Some minifier keep header comment over its format.

1. YUI Compressor
It keeps the header comments beggining with `/*!`
* http://yui.github.io/yuicompressor/css.html#special-comments

2. Closure compiler
It keeps the header comments containing `@license` or `@preserve`
* https://developers.google.com/closure/compiler/docs/js-for-compiler#tag-license

I think header comment is very important because it includes its own license.
Inspect `content` in assertion message of '#each' helper

I improved assetion message to inspect `content` of `#each` helper.

before:
> You passed [object Object] (wrapped in (generated ontology.index controller))

after:
> You passed '{}' (wrapped in (generated ontology.index controller))

"[object Object]" should be inspected for kindness of debugging.
Merge pull request #3865 from tricknotes/update-header-comment-format

Update header comment format to keep it on minify
Merge pull request #3866 from tricknotes/improve-assertion-message

Inspect `content` in assertion message of '#each' helper
[DOC beta] Clarify context of a component's block.