Add missing DECREF to PyErr_WriteUnraisable(). That function reports exceptions that can't be raised any further, because (for instance) they occur in __del__ methods. The coroutine tests in test_generators was triggering this leak. Remove the leakers' testcase, and add a simpler testcase that explicitly tests this leak to test_generators. test_generators now no longer leaks at all, on my machine. This fix may also solve other leaks, but my full refleakhunting run is still busy, so who knows?

--- a/Python/errors.c	Sat Apr 15 22:59:10 2006 +0000
+++ b/Python/errors.c	Sat Apr 15 23:27:28 2006 +0000
@@ -604,6 +604,7 @@
 				PyFile_WriteString(": ", f);
 				PyFile_WriteObject(v, f, 0);
 			}
+			Py_DECREF(moduleName);
 		}
 		PyFile_WriteString(" in ", f);
 		PyFile_WriteObject(obj, f, 0);