Fix test_import failure when run multiple times.

(2.7-only)

Author: pitrou

Lib/test/test_import.py

@@ -263,7 +263,10 @@ def __del__(self):
                   import imp
             sys.argv.insert(0, C())
             """))
-        script_helper.assert_python_ok(testfn)
+        try:
+            script_helper.assert_python_ok(testfn)
+        finally:
+            unlink(testfn)
 
     def test_bug7732(self):
         source = TESTFN + '.py'