Add Error#full_message test; Fix typos

Introduce test on Error#full_message for attribute with underscores; Fix
some typos

activemodel/test/cases/errors_test.rb

@@ -225,6 +225,7 @@ def test_has_key?
   test 'full_message should return the given message with the attribute name included' do
     person = Person.new
     assert_equal "name can not be blank", person.errors.full_message(:name, "can not be blank")
+    assert_equal "name_test can not be blank", person.errors.full_message(:name_test, "can not be blank")
   end
 
   test 'should return a JSON hash representation of the errors' do

activerecord/test/cases/base_test.rb

@@ -1024,7 +1024,7 @@ def test_dont_clear_sequence_name_when_setting_explicitly
     Joke.reset_sequence_name
   end
 
-  def test_dont_clear_inheritnce_column_when_setting_explicitly
+  def test_dont_clear_inheritance_column_when_setting_explicitly
     Joke.inheritance_column = "my_type"
     before_inherit = Joke.inheritance_column
 

activerecord/test/cases/nested_attributes_test.rb

@@ -806,7 +806,7 @@ def test_can_use_symbols_as_object_identifier
     assert_nothing_raised(NoMethodError) { @pirate.save! }
   end
 
-  def test_numeric_colum_changes_from_zero_to_no_empty_string
+  def test_numeric_column_changes_from_zero_to_no_empty_string
     Man.accepts_nested_attributes_for(:interests)
 
     repair_validations(Interest) do