If the user explicitly disables the basic security features and forgets to
@EnableWebSecurity, and yet still wants a bean of type
WebSecurityConfigurerAdapter, he is trying to use a custom
security setup and the app would fail in a confusing way without
this change.
Fixes gh-568
If the user sets security.basic.enabled=false he has to remember
to @EnableWebSecurity. Possibly we could be more helpful about the
exception, but I think this might be pilot error.
Fixes gh-568
