skip some test for storage backends that don't support touch

tests/lib/filestorage.php

@@ -176,8 +176,9 @@ abstract class Test_FileStorage extends UnitTestCase {
 		$this->assertEqual($stat['ctime'],$cTime);
 		
 		$mtimeStart=time();
-		$this->instance->touch('/lorem.txt');
+		$supportsTouch = $this->instance->touch('/lorem.txt');
 		$mtimeEnd=time();
+		if($supportsTouch !== false){
 			$originalCTime=$cTime;
 			$cTime=$this->instance->filectime('/lorem.txt');
 			$mTime=$this->instance->filemtime('/lorem.txt');
@@ -191,6 +192,7 @@ abstract class Test_FileStorage extends UnitTestCase {
 				$mTime=$this->instance->filemtime('/lorem.txt');
 				$this->assertEqual($mTime,100);
 			}
+		}
 
 		$mtimeStart=time();
 		$fh=$this->instance->fopen('/lorem.txt','a');