Fix table_name in ActiveRecord with more than one abstract ancestors

When subclassing abstract_class table_name should be always computed
based on class name, no matter if superclass is subclassing base
or another abstract_class. So:

class FirstAbstract < ActiveRecord::Base
  self.abstract_class = true
end
class SecondAbstract < FirstAbstract
  self.abstract_class = true
end

class Post < SecondAbstract
  self.table_name #=> 'posts' (not 'second_abstracts')
end

activerecord/lib/active_record/model_schema.rb

@@ -139,10 +139,14 @@ module ActiveRecord
 
       # Computes the table name, (re)sets it internally, and returns it.
       def reset_table_name #:nodoc:
-        if superclass.abstract_class?
+        if abstract_class?
+          self.table_name = if superclass == Base || superclass.abstract_class?
+                              nil
+                            else
+                              superclass.table_name
+                            end
+        elsif superclass.abstract_class?
           self.table_name = superclass.table_name || compute_table_name
-        elsif abstract_class?
-          self.table_name = superclass == Base ? nil : superclass.table_name
         else
           self.table_name = compute_table_name
         end

activerecord/test/cases/base_test.rb

@@ -27,6 +27,13 @@ require 'rexml/document'
 require 'active_support/core_ext/exception'
 require 'bcrypt'
 
+class FirstAbstractClass < ActiveRecord::Base
+  self.abstract_class = true
+end
+class SecondAbstractClass < FirstAbstractClass
+  self.abstract_class = true
+end
+class Photo < SecondAbstractClass; end
 class Category < ActiveRecord::Base; end
 class Categorization < ActiveRecord::Base; end
 class Smarts < ActiveRecord::Base; end
@@ -2088,4 +2095,8 @@ class BasicsTest < ActiveRecord::TestCase
     Bird.stubs(:scoped).returns(mock(:uniq => scope))
     assert_equal scope, Bird.uniq
   end
+
+  def test_table_name_with_2_abstract_subclasses
+    assert_equal "photos", Photo.table_name
+  end
 end