Expand var-args before passing to KeyGenerator

Update `CacheAspectSupport` to expand any var-arg parameters before
calling `KeyGenerator` implementations. Prior to this commit var-args
would be passed to `KeyGenerator` implementations as a nested array,
often causing the same key to be generated regardless of the arguments.

Issue: SPR-10870

spring-context/src/test/java/org/springframework/cache/config/AbstractAnnotationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2013 the original author or authors.
+ * Copyright 2002-2013 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -211,6 +211,19 @@ public abstract class AbstractAnnotationTests {
 		assertNotSame(r3, r4);
 	}
 
+	public void testVarArgsKey(CacheableService<?> service) throws Exception {
+		Object r1 = service.varArgsKey(1, 2, 3);
+		Object r2 = service.varArgsKey(1, 2, 3);
+
+		assertSame(r1, r2);
+
+		Object r3 = service.varArgsKey(1, 2, 3);
+		Object r4 = service.varArgsKey(1, 2);
+
+		assertNotSame(r3, r4);
+	}
+
+
 	public void testNullValue(CacheableService<?> service) throws Exception {
 		Object key = new Object();
 		assertNull(service.nullValue(key));
@@ -478,6 +491,11 @@ public abstract class AbstractAnnotationTests {
 		testKeyExpression(cs);
 	}
 
+	@Test
+	public void testVarArgsKey() throws Exception {
+		testVarArgsKey(cs);
+	}
+
 	@Test
 	public void testClassCacheCacheable() throws Exception {
 		testCacheable(ccs);

spring-context/src/test/java/org/springframework/cache/config/AnnotatedClassCacheableService.java

@@ -89,6 +89,12 @@ public class AnnotatedClassCacheableService implements CacheableService<Object>
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable(value = "default")
+	public Object varArgsKey(Object... args) {
+		return counter.getAndIncrement();
+	}
+
 	@Override
 	@Cacheable(value = "default", key = "#root.methodName + #root.caches[0].name")
 	public Object name(Object arg1) {

spring-context/src/test/java/org/springframework/cache/config/CacheableService.java

@@ -44,6 +44,8 @@ public interface CacheableService<T> {
 
 	T key(Object arg1, Object arg2);
 
+	T varArgsKey(Object... args);
+
 	T name(Object arg1);
 
 	T nullValue(Object arg1);

spring-context/src/test/java/org/springframework/cache/config/DefaultCacheableService.java

@@ -91,6 +91,12 @@ public class DefaultCacheableService implements CacheableService<Long> {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable(value = "default")
+	public Long varArgsKey(Object... args) {
+		return counter.getAndIncrement();
+	}
+
 	@Override
 	@Cacheable(value = "default", key = "#root.methodName")
 	public Long name(Object arg1) {