fix(Angular.js): restore shallowCopy properties fitlering condition

in angular version >= 1.2.6 shallowCopy also filtered properties
prefixed with a single `$`
Problem cames from the upgrade of the condition to filter properties
that have a '$$' prefix (See commit cb29632).

Restore the behavior shallowCopy had in angular 1.2.5 and previous
versions.