Fix test_novice.test_update_on_save failure on Windows

On Windows, tempfile.NamedTemporaryFile() can not be opened a second time. See <http://docs.python.org/2/library/tempfile.html#tempfile.NamedTemporaryFile>

skimage/novice/tests/test_novice.py

@@ -111,12 +111,16 @@ def test_update_on_save():
     assert pic.modified
     assert pic.path is None
 
-    with tempfile.NamedTemporaryFile(suffix=".jpg") as tmp:
-        pic.save(tmp.name)
+    fd, filename = tempfile.mkstemp(suffix=".jpg")
+    os.close(fd)
+    try:
+        pic.save(filename)
 
         assert not pic.modified
-        assert_equal(pic.path, os.path.abspath(tmp.name))
+        assert_equal(pic.path, os.path.abspath(filename))
         assert_equal(pic.format, "jpeg")
+    finally:
+        os.unlink(filename)
 
 
 def test_indexing():