Skip test_imp if threading is not available.

Closes bug #1083645.  Thanks Detlef Vollmann.
diff --git a/Lib/test/test_imp.py b/Lib/test/test_imp.py
index 9b7e3b7..893ba24 100644
--- a/Lib/test/test_imp.py
+++ b/Lib/test/test_imp.py
@@ -1,5 +1,9 @@
 import imp
-from test.test_support import TestFailed
+from test.test_support import TestFailed, TestSkipped
+try:
+    import thread
+except ImportError:
+    raise TestSkipped("test only valid when thread support is available")
 
 def verify_lock_state(expected):
     if imp.lock_held() != expected: