Add spring-build 2.5.2

spring-build was previously included via an svn:external. Adding
directly to the source tree under Git to avoid the need for a git
submodule.

In order to build from any earlier commit, it is recommended to
export spring-build or symlink an existing copy into the root
of the spring-framework project and then build normally.

    $ svn export https://src.springsource.org/svn/spring-build/tags/project-build-2.5.2 spring-build

.gitignore

@@ -14,5 +14,4 @@ org.springframework.jdbc/derby.log
 org.springframework.spring-parent/.classpath
 org.springframework.spring-parent/.project
 org.springframework.test/test-output/
-spring-build
 target