avoid confusing docs about autoload return value

autoload return value has no effect on other autoloaders
they will only be called based on whether the class has been loaded or
not.

framework/yii/YiiBase.php

@@ -339,9 +339,10 @@ class YiiBase
 	 *    it will attempt to include the file associated with the corresponding path alias
 	 *    (e.g. `@PHPUnit/Framework/TestCase.php`);
 	 * 4. Search PHP include_path for the actual class file if [[enableIncludePath]] is true;
-	 * 5. Return false so that other autoloaders have chance to include the class file.
+	 * 5. If none of the above succeeds, do nothing so that other autoloaders have the chance
+	 *    to load the class.
 	 *
-	 * @param string $className the fully qualified class name without leading \
+	 * @param string $className the fully qualified class name without leading backslash
 	 * @return boolean whether the class has been loaded successfully
 	 * @throws UnknownClassException if the class does not exist in the class file
 	 */
@@ -376,7 +377,8 @@ class YiiBase
 			}
 
 			if (!isset($classFile)) {
-				// return false to let other autoloaders to try loading the class
+				// return here, not trying to include a file to
+				// let other autoloaders try loading the class
 				return false;
 			}
 		}