Fix APC registration for @EnableTransactionManagement

Prior to this change, @EnableTransactionManagement (via the
ProxyTransactionManagementConfiguration class) did not properly
register its auto-proxy creator through the usual AopConfigUtils
methods.  It was trying to register the APC as a normal @Bean method,
but this causes issues (SPR-8494) with the logic in
AopConfigUtils#registerOrEscalateApcAsRequired, which expects the APC
bean definition to have a beanClassName property.  When the APC is
registered via a @Bean definition, it is actually a
factoryBean/factoryMethod situation with no directly resolvable
beanClass/beanClassName.

Rather than trying to rework how AopConfigUtils works, a @PostConstruct
method has been added to ProxyTransactionManagementConfiguration to call
the usual AopConfigUtils registration methods.

Issue: SPR-8411, SPR-8494

org.springframework.integration-tests/src/test/resources/org/springframework/transaction/annotation/enable-caching.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xmlns:cache="http://www.springframework.org/schema/cache"
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
+		http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd">
+
+	<cache:annotation-driven/>
+
+</beans>