revised titles in validation and callbacks guide

railties/guides/source/activerecord_validations_callbacks.textile

@@ -1030,7 +1030,7 @@ h3. Observers
 
 Observers are similar to callbacks, but with important differences. Whereas callbacks can pollute a model with code that isn't directly related to its purpose, observers allow you to add the same functionality outside of a model. For example, it could be argued that a +User+ model should not include code to send registration confirmation emails. Whenever you use callbacks with code that isn't directly related to your model, you may want to consider creating an observer instead.
 
-h4. Creating observers
+h4. Creating Observers
 
 For example, imagine a +User+ model where we want to send an email every time a new user is created. Because sending emails is not directly related to our model's purpose, we could create an observer to contain this functionality.