If a resource is being fetched, .fetch should not return a resolved
promise

It should instead return the same deferred promise as the pending AJAX
call.

Before:

a = resource.fetch();
b = resource.fetch();
a === b; //false
a.state(); //resolved

After:

a = resource.fetch();
b = resource.fetch();
a === b; //true
a.state(); //pending
fetch when isFetching: return a promise, and not a $.Deferred instance
Merge pull request #72 from zendesk/shajith/fetching

If a resource is being fetched, .fetch should not return a resolved promise