Fix remaining Java compiler warnings, mainly around missing
generics or deprecated code.

Also add the `-Werror` compiler option to ensure that any future
warnings will fail the build.

Issue: SPR-11064

This commit undoes the changes made in ec5d81e7 and ensures that the
getRequestURL() method in MockHttpServletRequest does not include the
String "null" for a null requestURI by first checking if the requestURI
contains text before including it in the composed URL.

Issue: SPR-10643

Prior to this commit it was possible for the method and requestURI
fields in MockHttpServletRequest to be set to null.

This commit ensures that the method and requestURI fields are internally
stored as empty strings if the user sets them to a null value.

Issue: SPR-10643

Prior to this commit, MockHttpServletRequest.getRequestURL() always
included the server port number in the reconstructed request URL, even
for implicit ports (i.e., 80 and 443) and negative ports.

MockHttpServletRequest.getRequestURL() now omits the port number when
reconstructing a URL that has an implicit or negative port.

Issue: SPR-9726

Issue: SPR-10130

Upgraded all Servlet API mocks to Servlet 3.0 (with a little bit of Servlet 3.1 support in MockHttpServletResponse)

Consistent use of LinkedHashMaps and independent getAttributeNames Enumeration in Servlet/Portlet mocks

Issue: SPR-10224

Issue: SPR-10192

This reverts commit 45fa5082, reversing
changes made to a312d900.

Issue: SPR-10130

Issue: SPR-10128

  find . -type f -name "*.java" -or -name "*.aj" | \
    xargs perl -p -i -e "s/[ \t]*$//g" {} \;

Issue: SPR-10127

Prior to this commit the MockHttpServletRequest constructor chain set
the preferred local to Locale.ENGLISH. Furthermore, it was possible to
add additional preferred locales "in front" of ENGLISH; however, it was
not possible to delete ENGLISH from the list of preferred locales.

This commit documents the fact that ENGLISH is the default preferred
locale and makes it possible to set the list of preferred locales via a
new setPreferredLocales(List<Locale> locales) method.

Issue: SPR-9724

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

The initial solution kept these three in full sync at all times:
contentType field, characterEncoding field, 'Content-Type' header.
That is correct behavior, however it breaks existing tests that rely
on contentType and characterEncoding being equal to exactly what 
they were set to.

For example, consider:
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");

Ideally both contentType and the 'Content-Type' header would now be
"text/plain;charset=UTF-8". However, existing tests would expect 
that contentType is equal to "text/plain".

To avoid breaking existing tests, contentType and characterEncoding
will continue to be equal to exactly what they were set to while
the 'Content-Type' header will always include both the content 
type and the charset.

The only exception to this rule is when a 'Content-Type' header
is set explicitly, the contentType and characterEncoding fields will 
be updated accordingly, possibly overriding the existing values.

The Content-Type header and the contentType field in HttpServletRequest/Response
are now always in sync. When a header is added the contentType field is updated
as well and vice versa. 

Similarly when the Content-Type header or the contentType field includes a charset 
field, the character encoding is updated and vice versa.

extended Servlet API mocks for Servlet 3.0 forward compatibility as far as possible; made MockHttpServletResponse compatible with Servlet 3.0 getHeader(s) method returning Strings (SPR-8529); added getHeaderValue(s) method to MockHttpServletResponse for raw value access

replaced Commons Collections dependency with Spring-provided LinkedCaseInsensitiveMap; revised CollectionFactory and Spring Map implementations for consistency

EL container integration; support for contextual objects; removal of deprecated Spring 2.0 functionality; Java 5 code style