Issue: SPR-10930

After this change, annotated message handling methods configured to use
a destination prefix (e.g. "/app") no longer have to include the prefix
in their mapping. For example if a client sends a message to "/app/foo"
the annotated methods should be mapped with @MessageMapping("/foo").

Issue: SPR-10835

Consolidates new, messaging-related classes from spring-context and
spring-websocket into one module.

This renaming more intuitively expresses the relationship between
subprojects and the JAR artifacts they produce.

Tracking history across these renames is possible, but it requires
use of the --follow flag to `git log`, for example

    $ git log spring-aop/src/main/java/org/springframework/aop/Advisor.java

will show history up until the renaming event, where

    $ git log --follow spring-aop/src/main/java/org/springframework/aop/Advisor.java

will show history for all changes to the file, before and after the
renaming.

See http://chrisbeams.com/git-diff-across-renamed-directories

RESOLVED - issue SPR-6779: imported @Configuration classes do not get enhanced and fail to satisfy scoping requirements
refactoring, polishing.

IN PROGRESS - issue SPR-6779: imported @Configuration classes do not get enhanced and fail to satisfy scoping requirements
All tests in ImportedConfigurationClassEnhancementTests now pass.  The fix was simple - imported @Configuration class bean definitions were not getting marked with the attribute that indicates that they are indeed @Configuration class bean definitions.  To make this happen, ConfigurationClassPostProcessor's protected checkConfigurationClassCandidate(beanDef) method is being called from within ConfigurationClassBeanDefinitionReader when imported @Configuration classes are being processed.  This is quick and dirty, and the subsequent check-in will refactor the solution appropriately.

added conversion service performance optimizations; added mapping cyclical ref handling; removed ConverterInfo in favor of specifying S and T at registration time if necessary