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

isCglibProxy* methods in AopUtils are useful in lower-level modules,
i.e. those that cannot depend on .aop.  Therefore copied these methods
to ClassUtils; deprecated the existing ones in AopUtils and now
delegating to the new location; switched all usage of
AopUtils#isCglibProxy* within the framework to use
ClassUtils#isCglibProxy* instead.

added "expose-proxy" attribute to aop namespace (enforcing AopContext proxy exposure with CGLIB; SPR-7261)