Added assertion for updateLink

Added an assertion for string type. Since you could also pass objects
to `updateLink` (which would always result in false in the next if
statement) containing a link. This PR notifies creators of serializers
so they always use a string when handling links.

Added test for links with type other than string
Removed a duplicate line.
Added test case for push link with null value
Remove unnecessary `Function#call`
[DOC] Fix to apply js doc style to DS.ManyArray
[DOC] Fix usage of DS.Model.fields

`DS.Model.fields` is a `Ember.Map`.
Its behavior changed at 2eb1c971 .
Merge pull request #2388 from tricknotes/doc

[DOC] Fix to apply js doc style
Merge pull request #2387 from tricknotes/remove-unnecessary-call

Remove unnecessary `Function#call`
Make dependencies clearer.

This is mostly just for easier discovery/understanding for passers by
looking at the `bower.json` in the root of the repo. The actual
`bower.json` that we put in components/ember-data is correct already.
Merge pull request #2390 from rwjblue/deps

Make dependencies clearer.
Refactored InvalidError handling into a serializer concern.
Merge pull request #2392 from ahacking/serialization-for-invalid-error

Refactored InvalidError handling into a serializer concern.
Merge pull request #2354 from steffenbrem/update-links-assert-fix

Added assertion for updateLink
Fixing an issue when grouping requests could result in URL longer than configured length.
Merge pull request #2396 from grishace/uri_encoded_brackets

Fixing an issue when grouping requests could result in long URL
Nicer errors when pushing belongsTo/hasMany with invalid values
Merge pull request #2377 from wecc/nicer-push-errors

Nicer errors when pushing belongsTo/hasMany with invalid values
Fixes method_ajaxError link

Currently links to http://emberjs.com/api/data/classes/api/data/classes/DS.RESTAdapter.html#method_ajaxError 
Please review.
Merge pull request #2397 from vladikoff/patch-1

Fixes method_ajaxError link
disable canary until we figure out how to load Hbs

canary recently introduced Handlebars 2.0, and that's why canary is currently failing.
load handlebars 2.0 for canary
Merge pull request #2404 from emberjs/fix-travis-for-handlebars-2.0

load handlebars 2.0 for canary