Ensure the correct ordering of links for more complex joins

Consider a query like the following:

Person.all(Person.memberships.group.type => 'cool', Person.memberships.valid_from.gte => Date.today)

This can result in one of the following to link lists being set up (depending on non-deterministic
hash ordering).

[:memberships, :group, :memberships]
[:group, :memberships, :memberships]

Query#normalize_links walks through this list and creates the following structure:

[:memberships, :group] or [:group, :memberships]

If the first situation happens and the subsequent join statement is created, it will
create an invalid join statement. DataObjectsAdapter#join_statement walks through
the normalized list in revere order, so if that adds group to the query before
memberships in a join, the query will fail.

The fix is very simple. Because of how the initial list is constructed, a correctly
normalized list will be created by walking the initial 3 element list given above in the
reverse order. That will always result in the [:group, :memberships] links that
will work correctly if joined in reverse order

lib/dm-core/query.rb

@@ -925,7 +925,7 @@ def normalize_links
 
       @links.clear
 
-      while link = links.shift
+      while link = links.pop
         relationship = case link
           when Symbol, String             then @relationships[link]
           when Associations::Relationship then link
@@ -961,6 +961,7 @@ def normalize_links
           @links << relationship
         end
       end
+      @links.reverse!
     end
 
     # Append conditions to this Query