Improving method validation support for BV 1.1

Update MethodValidationPostProcessor.setValidator(...) to use
LocalValidatorFactoryBean.getValidator() when possible.

This is required because LocalValidatorFactoryBean does not directly
implement the forExecutables() method introduced in bean validation v1.1.

Issue: SPR-10644

spring-context/src/main/java/org/springframework/validation/beanvalidation/MethodValidationPostProcessor.java

@@ -83,8 +83,13 @@ public class MethodValidationPostProcessor extends AbstractAdvisingBeanPostProce
 	 * <p>Default is the default ValidatorFactory's default Validator.
 	 */
 	public void setValidator(Validator validator) {
+		if(validator instanceof LocalValidatorFactoryBean) {
+			this.validator = ((LocalValidatorFactoryBean) validator).getValidator();
+		}
+		else {
 			this.validator = validator;
 		}
+	}
 
 	/**
 	 * Set the JSR-303 ValidatorFactory to delegate to for validating methods,