Fix imread regression for int16 images with PIL plugin.

Regression introduced in PR 101.

skimage/io/_plugins/pil_plugin.py

@@ -23,7 +23,7 @@ def imread(fname, dtype=None):
             im = im.convert('RGB')
     elif im.mode == '1':
         im = im.convert('L')
-    elif im.mode == 'I;16':
+    elif im.mode.startswith('I;16'):
         shape = im.size
         dtype = '>u2' if im.mode.endswith('B') else '<u2'
         im = np.fromstring(im.tostring(), dtype)