Upgrade to coverage 3.7.1 and have it auto-build itself on first use.

third_party/coverage-3.7.1/coverage/__init__.py

Index: third_party/coverage-3.7.1/coverage/__init__.py
diff --git a/third_party/coverage-3.6/coverage/__init__.py b/third_party/coverage-3.7.1/coverage/__init__.py
similarity index 98%
rename from third_party/coverage-3.6/coverage/__init__.py
rename to third_party/coverage-3.7.1/coverage/__init__.py
index 0ccc699f1311b3fc94333c67a9a1d0db5bc29528..193b7a107ebd3716e69333d11df05537c8208ed3 100644
--- a/third_party/coverage-3.6/coverage/__init__.py
+++ b/third_party/coverage-3.7.1/coverage/__init__.py
@@ -92,7 +92,7 @@ except KeyError:
 # COPYRIGHT AND LICENSE
 #
 # Copyright 2001 Gareth Rees.  All rights reserved.
-# Copyright 2004-2012 Ned Batchelder.  All rights reserved.
+# Copyright 2004-2013 Ned Batchelder.  All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are