Restore the ability to create a TypeDescriptor for a collection or
map where the generics may be null.

Issue: SPR-11006

Refactor TypeDescriptor to use ResolvableType in order to retain full
generic type information, in the process fixing MultiValueMap support
in MapToMapConverter.

Issue: SPR-9499

Issue: SPR-10631

Issue: SPR-10130

- fix @since version in array()
- format method-level Javadoc
- unescape HTML-escaped angle brackets with {@code} blocks

Add a static factory method that can be used to create an array
TypeDescriptor with a specific element type. Allows array types
with generic elements to be constructed.

Issue: SPR-9792

Issue: SPR-10128

Content:

 - Rename Conditional{Conversion=>Converter}
 - Add @since tags where appropriate
 - Update Apache date headers to read 2002-2012 (not just 2012)
 - Correct minor Javadoc typo

Style:

 - Polish line breaks / whitespace
 - Use wildcard static imports where appropriate

Issue: SPR-9566, SPR-9692, SPR-9928, SPR-9927

Refactor internal workings of GenericConversionService in order to
better support future enhancements. This commit should not affect
existing behavior.

Issue: SPR-9927

- Use generic typing for getAnnotation()
- Add hasAnnoation() method
- Update existing code and tests to make use of changes

Issue: SPR-9744

- Remove trailing whitespace
- Apply consistent JavaDoc formatting

Before this change there were numerous javadoc warnings being reported
while building Spring framework API.

This commit resolves most of the javadoc warnings, reducing the total
number from 265 to 103.

Issue: SPR-9113

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

renamed mapKey/ValueTypeDescriptor methods back to getMapKey/ValueTypeDescriptor (for Spring 3.0.x compatibility)

restored TypeDescriptor getElementType, getMapKeyType, and getMapValueType compatibility; StringToCollection and Array Converters are now conditional and check targetElementType if present; TypeDesciptor#isAssignable no longer bothers with element type and map key/value types in checking assignability for consistency elsewhere; improved javadoc

simplified TypeDescriptor usage and updated use of the API across BeanWrapper and SpEL; collapsed PropertyTypeDescriptor into TypeDescriptor for simplicity and ease of use; improved docs

revised findCommonElement handling within TypeDescriptor.forObject(Object); we now fully introspect the collection elements to resolve the common type.  We also support nested introspection e.g. collections of collections.  Object.class is used to indicate no common type, and TypeDescriptor.NULL is used to indicate a null element value