Missing import in test_curses, uncovered by some buildbots.

(There are still a few test files that don't use the standard layout)

Lib/test/test_curses.py

@@ -15,6 +15,7 @@ import sys, tempfile, os
 # 'curses' resource be given on the regrtest command line using the -u
 # option.  If not available, nothing after this line will be executed.
 
+import unittest
 from test.test_support import requires, import_module
 requires('curses')
 curses = import_module('curses')