Given that Spring Boot uses java config accross the board, a new `value`
attribute is now aliased to the existing `classes` attribute such that
one could write the following:
@SpringApplicationConfiguration(MyConfig.class)
public class MyTest {}
Closes gh-3635
Up to now we have been treating the *first* class to be compiled
as the "main" application and adding @EnableAutoConfiguration. This
isn't always appropriate (e.g. if it's a test case), so now we
look for an appropriate annotation before falling back to the old
behaviour.
In addition ensures classes with a field of type Reactor trigger
the reactor auto imports.
See gh-969
Andy Wilkinson
Stephane Nicoll
Dave Syer
Phillip Webb