fix(ngResource): restore shallowClearAndCopy properties fitlering condition


Change the way properties are fitlered to create a resource from a
JavaScript Object.

in angular version >= 1.2.6 properties of a resource with a name
beginning by a single '$' were fitlered from the created resource.
Problem cames from the upgrade of the condition to filter properties that
have a '$$' prefix in the shallow copy. See commit cb29632.

Restore the behavior ngResource had in angular 1.2.5 and inferior
versions.