Be smarter about get/getPath usage

Ember 0.9's getPath has been deprecated in 1.0 and replaced with get.
Since 0.9 also has get, but it behaves differently, we do some behavior
detection to define Ember.Resource.getPath and use that everywhere.

One test also uses setPath, so we do a similar behavior detection in
just that test.
Make specs compatible with 1.0.rc7

In Ember 1.0, `Ember.Object.create` no longer supports

 * defining computed properties
 * defining observers
 * defining functions that call _super

The specs were doing these. This commit replaces those calls with
`.extend(...).create()`. It *could* have instead used
`.createWithMixins`, but that function doesn't exist in Ember 0.9.8.1,
which this version of Ember-Resource also supports.
Merge pull request #40 from zendesk/james/ember_1_0

Ember 1.0 Compatibility