Disable bean overriding by default and provide a configuration property to enable it

[wilkinsona]

From what we've seen, overriding one bean definition with another (by providing two definitions with the same name) is most often done accidentally. When it is done, the info log message is almost always missed, leading to hard to diagnose behaviour. We should disable bean overriding by default and provide a configuration property to turn it back on along with failure analysis of the exception that clearly describes the problem and suggests setting the property as a possible action.

[wilkinsona]

Currently, a rejected override attempt results in a BeanDefinitionStoreException. It would be very useful for failure analysis if a specific exception was thrown that provided access to both the existing and the overriding bean definitions. I've opened https://jira.spring.io/browse/SPR-16982.

[spencergibb]

We've similarly dealt with some issues with this in spring cloud

[wilkinsona]

This broke the build and fixing it is blocked by #13737.

[wilkinsona]

With #13737 fixed, this is still blocked but by Spring Data REST now. It tries to override a bean that's already been defined by Spring MVC.