SEC-1369: Make sure beans aren't registered twice in case allowBeanDefinitionOverriding=false in the app context.

The use of registerBeanComponent() also registers the bean definition, which causes an error if overriding is disallowed and the bean has already been registered using registerBeanDefinition(). I've also set the allowBeanDefinitionOverriding to 'false' on InMemoryXmlApplicationContext to detect future mistakes of this kind in testing.

config/src/test/java/org/springframework/security/config/util/InMemoryXmlApplicationContext.java

@@ -32,6 +32,7 @@ public class InMemoryXmlApplicationContext extends AbstractXmlApplicationContext
     public InMemoryXmlApplicationContext(String xml, String secVersion, ApplicationContext parent) {
         String fullXml = BEANS_OPENING + secVersion + ".xsd'>\n" + xml + BEANS_CLOSE;
         inMemoryXml = new InMemoryResource(fullXml);
+        setAllowBeanDefinitionOverriding(false);
         setParent(parent);
         refresh();
     }