Includes refinements for consistent quoting of names in exception messages.

Issue: SPR-13972

Update SpringFactoriesLoader so that package private classes can be
used.

Issue: SPR-13969

Closes gh-934

Refine the optimizations made in 6f55ab69 in order to restore binary
compatibility and resolve a regression.

Tests of the form pathMatcher.match("/foo/bar/**", "/foo/bar") should
return true as this was the behavior in Spring 4.2.

Issue: SPR-13913

This commit speeds up the AntPathMatcher implementation by
pre-processing patterns and checking that candidates are likely
matches if they start with the static prefix of the pattern.

Those changes can result in a small performance penalty for positive
matches, but with a significant boost for checking candidates that don't
match. Overall, this tradeoff is acceptable since this feature is often
used to select a few matching patterns in a much bigger list.

This will lead to small but consistent performance improvements in
Spring MVC when matching a given request with the available routes.

Issue: SPR-13913

Issue: SPR-13344

Issue: SPR-13828

Issue: SPR-13594

Issue: SPR-13713

Issue: SPR-13714

- Delete unused imports
- Delete unused code
- Clean up warnings

JIRA: https://jira.spring.io/browse/SPR-13784

JDK8 and Apache Commons Codec support the RFC 4648
"URL and Filename Safe" Base64 alphabet.

Add methods to `Base64Utils` to support this feature.

Issue: SPR-13696

Includes polishing of related conversion exception messages.

Issue: SPR-13703

Issue: SPR-13621

Issue: SPR-13393
(cherry picked from commit 302a0692)

Issue: SPR-13393

Issue: SPR-13554

Issue: SPR-13542

This commit migrates all remaining tests from JUnit 3 to JUnit 4, with
the exception of Spring's legacy JUnit 3.8 based testing framework that
is still in use in the spring-orm module.

Issue: SPR-13514

Issue: SPR-13509

This commit picks up where 3eacb837
(SPR-13345) left off by adding support for transitive implicit aliases
configured via @AliasFor.

Issue: SPR-13405

Spring Framework 4.2 introduced support for aliases between annotation
attributes that fall into the following two categories.

1) Alias pairs: two attributes in the same annotation that use
   @AliasFor to declare that they are explicit aliases for each other.
2) Meta-annotation attribute overrides: an attribute in one annotation
   uses @AliasFor to declare that it is an explicit override of an
   attribute in a meta-annotation.

However, the existing functionality fails to support the case where two
attributes in the same annotation both use @AliasFor to declare that
they are both explicit overrides of the same attribute in the same
meta-annotation. In such scenarios, one would intuitively assume that
two such attributes would be treated as "implicit" aliases for each
other, analogous to the existing support for explicit alias pairs.
Furthermore, an annotation may potentially declare multiple aliases
that are effectively a set of implicit aliases for each other.

This commit introduces support for implicit aliases configured via
@AliasFor through an extensive overhaul of the support for alias
lookups, validation, etc. Specifically, this commit includes the
following.

- Introduced isAnnotationMetaPresent() in AnnotationUtils.

- Introduced private AliasDescriptor class in AnnotationUtils in order
  to encapsulate the parsing, validation, and comparison of both
  explicit and implicit aliases configured via @AliasFor.

- Switched from single values for alias names to lists of alias names.

- Renamed getAliasedAttributeName() to getAliasedAttributeNames() in
  AnnotationUtils.

- Converted alias map to contain lists of aliases in AnnotationUtils.

- Refactored the following to support multiple implicit aliases:
  getRequiredAttributeWithAlias() in AnnotationAttributes,
  AbstractAliasAwareAnnotationAttributeExtractor,
  MapAnnotationAttributeExtractor, MergedAnnotationAttributesProcessor
  in AnnotatedElementUtils, and postProcessAnnotationAttributes() in
  AnnotationUtils.

- Introduced numerous tests for implicit alias support, including
  AbstractAliasAwareAnnotationAttributeExtractorTestCase,
  DefaultAnnotationAttributeExtractorTests, and
  MapAnnotationAttributeExtractorTests.

- Updated Javadoc in @AliasFor regarding implicit aliases and in
  AnnotationUtils regarding "meta-present".

Issue: SPR-13345

SocketUtils is used to find available ports on localhost; however,
prior to this commit, SocketUtils incorrectly reported a port as
available on localhost if another process was already bound to
localhost on the given port but not to other network interfaces. In
other words, SocketUtils determined that a given port was available for
some interface though not necessarily for the loopback interface.

This commit addresses this issue by refactoring SocketUtils so that it
tests the loopback interface to ensure that the port is actually
available for localhost.

Issue: SPR-13321

Issue: SPR-13312

Issue: SPR-13312

This commit introduces an additional test case to ensure that explicit
local attribute aliases (configured via @AliasFor) do not accidentally
override attributes of the same names in meta-annotations (i.e., by
convention).

Issue: SPR-13325

Prior to this commit, attempting to synthesize an annotation from a map
of annotation attributes that contained nested maps instead of nested
annotations would result in an exception.

This commit addresses this issue by properly synthesizing nested maps
and nested arrays of maps into nested annotations and nested arrays of
annotations, respectively.

Issue: SPR-13338