Fix Traceback in backends/portalocker.py (windows)

.. due to missing windll import, thanks to Heiko Stegmann for suggesting
a first fix.

Author: schlatterbeck

CHANGES.txt

@@ -336,6 +336,8 @@ Fixed:
   Firefox. The old version would show the popup but after clicking away
   the alert it would load the page. The new version (tested with
   Chromium and Firefox) doesn't load the page.
+- Fix Traceback in backends/portalocker.py on windows due to missing
+  windll import, thanks to Heiko Stegmann for suggesting a first fix.
 
 
 2016-01-11: 1.5.1

doc/acknowledgements.txt

@@ -195,6 +195,7 @@ Alexander Smishlajev,
 Nathaniel Smith,
 Leonardo Soto,
 Maciej Starzyk,
+Heiko Stegmann,
 Kai Storbeck,
 Mitchell Surface,
 anatoly techtonik,

roundup/backends/portalocker.py

@@ -54,6 +54,7 @@
 if os.name == 'nt':
     import msvcrt
     import ctypes
+    from ctypes import windll
     from ctypes.wintypes import BOOL, DWORD, HANDLE
 
     LOCK_SH = 0    # the default