Update #finalize to always return self

* In general command methods like finalize will return self, as the DM API
  moves closer towards using CQS like Veritas, Virtus and other libraries
  that will be part of DM2.

lib/dm-core.rb

@@ -280,7 +280,7 @@ def self.repository(name = nil)
   # These are otherwise lazily declared, which can lead to unexpected errors.
   # It also performs basic validity checking of the DataMapper models.
   #
-  # @return [DataMapper] The DataMapper module
+  # @return [self]
   #
   # @api public
   def self.finalize

lib/dm-core/associations/many_to_many.rb

@@ -126,10 +126,13 @@ def links
 
         # Initialize the chain for "many to many" relationships
         #
+        # @return [self]
+        #
         # @api public
         def finalize
           through
           via
+          self
         end
 
         # @api private

lib/dm-core/associations/many_to_one.rb

@@ -72,9 +72,12 @@ def child_key
         # Initialize the foreign key property this "many to one"
         # relationship uses to persist itself
         #
+        # @return [self]
+        #
         # @api public
         def finalize
           child_key
+          self
         end
 
         # Returns a hash of conditions that scopes query that fetches

lib/dm-core/associations/one_to_many.rb

@@ -104,6 +104,8 @@ def lazy_load(source)
         # initializing other relationships. This makes sure that foreign key
         # properties always appear in the order they were declared.
         #
+        # @return [self]
+        #
         # @api public
         def finalize
           child_model.relationships.each do |relationship|
@@ -114,6 +116,7 @@ def finalize
             end
           end
           inverse.finalize
+          self
         end
 
         # @api semipublic

lib/dm-core/model.rb

@@ -130,7 +130,7 @@ def raise_on_save_failure=(raise_on_save_failure)
 
     # Finish model setup and verify it is valid
     #
-    # @return [undefined]
+    # @return [self]
     #
     # @api public
     def finalize
@@ -139,6 +139,7 @@ def finalize
       assert_valid_name
       assert_valid_properties
       assert_valid_key
+      self
     end
 
     # Appends a module for inclusion into the model class after Resource.