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