RequiredAnnotationBeanPostProcessor's skip attribute accepts "true" as String value as well (SPR-8617)

[SPR-8386][SPR-8387] Refined logging regarding detection of default resource locations and default configuration classes.

- Removed generatesDefaults() and supports() from the SmartContextLoader SPI and modified the DelegatingSmartContextLoader algorithm accordingly.
- DelegatingSmartContextLoader no longer operates on a list of candidate loaders but rather on explicit instances of GenericXmlContextLoader and AnnotationConfigContextLoader.
- Updated Javadoc regarding DelegatingSmartContextLoader as the new default loader.
- Updated and polished Javadoc regarding changes in 3.1.
- Now enforcing @ContextConfiguration's restriction on declaring locations or classes but not both.

overridden @PersistenceContext annotations on subclass methods are being processed correctly (SPR-8594)

SPR-6464 Use the redirect URL and its request parameters (if any), instead of a synthetic key, to match a FlashMap instance to its intended recepient request. This should help to prevent conflicts in most cases transparently. Only if necessary a controller can add extra request parameters to distinguish the request even more uniquely.

Issue: SPR-8591

SPR-6464 Drop @FlashAttributes, add ResponseContext, ViewResponse, and RedirectResponse types for annotated controllers to use to prepare a redirect response with flash attributes; Add FlashMap and FlashMapManager and update DispatcherServlet to discover and invoke the FlashMapManager.

Issue: SPR-8579

removed GenericConversionService logging in order to avoid toString side effects (and to avoid isTraceEnabled overhead; SPR-8297)

Issue: SPR-8570

Replace RequestBodyNotValidException and RequestPartNotValidException with MethodArgumentNotValidException and add MethodParameter information to the exception message.

SPR-8536 When two methods match a request for any content type (i.e. Accept=*/* or no Accept header), choose the one that doesn't define any 'Accept' media types by default. This addresses an important use case where methods serving browsers typically don't specify Accept media types.