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

third_party/coverage-3.7.1/__main__.py

Index: third_party/coverage-3.7.1/__main__.py
diff --git a/third_party/coverage-3.7.1/__main__.py b/third_party/coverage-3.7.1/__main__.py
new file mode 100644
index 0000000000000000000000000000000000000000..b11dafce6d551111e7bf5a807cb6037beb448cc6
--- /dev/null
+++ b/third_party/coverage-3.7.1/__main__.py
@@ -0,0 +1,15 @@
+"""Be able to execute coverage.py by pointing Python at a working tree."""
+
+import runpy, os
+
+PKG = 'coverage'
+
+try:
+    run_globals = runpy.run_module(PKG, run_name='__main__', alter_sys=True)
+    executed = os.path.splitext(os.path.basename(run_globals['__file__']))[0]
+    if executed != '__main__':  # For Python 2.5 compatibility
+        raise ImportError(
+            'Incorrectly executed %s instead of __main__' % executed
+            )
+except ImportError:  # For Python 2.6 compatibility
+    runpy.run_module('%s.__main__' % PKG, run_name='__main__', alter_sys=True)