fix tests skip condition

tests/dlib_face_detection.phpt

@@ -1,7 +1,10 @@
 --TEST--
 Frontal face detection.
 --SKIPIF--
-<?php if (!extension_loaded("pdlib") print "skip"; ?>
+<?php
+if (!extension_loaded("pdlib"))  die('skip pdlib extension missing');
+if (getenv("SKIP_SLOW_TESTS")) die('skip slow test');
+?>
 --FILE--
 <?php
 printf("Simple detection\n");
@@ -25,4 +28,4 @@ Faces found = 1
 Face[0] in bounding box (left=214, top=194, right=393, bottom=373)
 Detection with upsampling
 Faces found = 1
-Face[0] in bounding box (left=201, top=180, right=386, bottom=366)
+Face[0] in bounding box (left=201, top=180, right=386, bottom=366)