improve getHasManyAttributeName algorithm

if some of the records are already loaded, then the array of ids sent to `getHasManyAttributeName` will not directly match the list of ids for the relationship.

This updates the `getHasManyAttributeName` method to match attributes that at least have the requested ids present instead of requiring a direct match.
Merge pull request #47 from craigteegarden/ember1.0-getHasManyAttributeName-error-when-some-records-already-loaded

Ember1.0 getHasManyAttributeName error when some records already loaded