…ribute

This is already handle if we get the toMany attribute of a record and
use pushObject. Like this: bar1.get('fooToMany').pushObject(foo2);

We this commit, the inverse relationships is also notify if we directly
set the attribute with an array. Like this:
bar1.set('fooToMany', [foo2, foo3]);

isSCArray is now used to check if the newRecords variable is an array.
This avoid an exception if we pass an SC.ManyArray because SC.typeOf
return 'object'.
If we pass null, transform it to an empty array. This will remove the
inverses relationship.