Turned Cache::buildKey() into public [skip ci]

framework/caching/Cache.php

@@ -80,7 +80,7 @@ abstract class Cache extends Component implements \ArrayAccess
      * @param mixed $key the key to be normalized
      * @return string the generated cache key
      */
-    protected function buildKey($key)
+    public function buildKey($key)
     {
         if (is_string($key)) {
             $key = ctype_alnum($key) && StringHelper::byteLength($key) <= 32 ? $key : md5($key);
@@ -141,7 +141,7 @@ abstract class Cache extends Component implements \ArrayAccess
      * Some caches (such as memcache, apc) allow retrieving multiple cached values at the same time,
      * which may improve the performance. In case a cache does not support this feature natively,
      * this method will try to simulate it.
-     * @param array $keys list of keys identifying the cached values
+     * @param string[] $keys list of string keys identifying the cached values
      * @return array list of cached values corresponding to the specified keys. The array
      * is returned in terms of (key, value) pairs.
      * If a value is not cached or expired, the corresponding array value will be false.