Have testLoadTkFailure() skip on cygwin since Tcl/Tk on cygwin renders to the

Windows GDI directly and thus does not need a DISPLAY environment variable.

Thanks Jason Tishler.

Lib/test/test_tcl.py

@@ -129,7 +129,9 @@ class TclTest(unittest.TestCase):
         import os
         old_display = None
         import sys
-        if sys.platform.startswith('win') or sys.platform.startswith('darwin'):
+        if (sys.platform.startswith('win') or
+                sys.platform.startswith('darwin') or
+                sys.platform.startswith('cygwin')):
             return # no failure possible on windows?
         if 'DISPLAY' in os.environ:
             old_display = os.environ['DISPLAY']