tests: Note that PILLOW_VERSION check also skips old Pillow

Author: bgilbert

tests/test_openslide.py

@@ -123,6 +123,7 @@ def test_read_region_bad_size(self):
                 lambda: self.osr.read_region((0, 0), 1, (400, -5)))
 
     @skip_if(sys.maxsize < 1 << 32, '32-bit Python')
+    # Also skips Pillow < 2.1.0
     @skip_if(have_optimizations and not hasattr(Image, 'PILLOW_VERSION'),
             'broken on PIL')
     def test_read_region_2GB(self):