Code was not adding foreign_type constraint

When we already had some constraints on the relation definition.

Ex, below case did not work:
  has_many :constraints, as: :restricted_object, integer_type: true,
           :conditions => { :is_deleted => false }

A workaround prior to this commit was to use the reverse mapping:
  has_many :constraints, as: :restricted_object, integer_type: true,
           :conditions => { :is_deleted => false, restricted_object_type: RESTRICTED_OBJECT_MAP_REVERSE[self.to_s] }
Merge pull request #5 from tispratik/master

Code was not adding foreign_type constraint