Test against CGLIB memory leak for method injection

This commit introduces a test in XmlBeanFactoryTests that verifies that
CGLIB generated subclasses for method injected beans are reused across
bean factories for identical bean definitions. In other words, by
verifying that the same CGLIB generated class is reused for identical
bean definitions, we can be certain that Spring is no longer generating
identical, duplicate classes that consume memory in the VM.

Issue: SPR-10785, SPR-11420
(cherry picked from commit f2a4537)
resolveFactoryMethodIfPossible considers nonPublicAccessAllowed and SecurityManager

Issue: SPR-11422
(cherry picked from commit 603cdea)
Polishing

Issue: SPR-11422
(cherry picked from commit 520ef9e)
Actually upgraded to Gradle 1.11
Fix imports in SourceHttpMessageConverterTests

Replaced static import of org.junit.Assert.* with implicit imports in
order to avoid ambiguity between JUnit's static Assert methods and those
in org.custommonkey.xmlunit.XMLAssert.