Adapt platform and test_platform to the build identification changes.
diff --git a/Lib/platform.py b/Lib/platform.py
index 7fba143..780301d 100755
--- a/Lib/platform.py
+++ b/Lib/platform.py
@@ -1373,7 +1373,9 @@
         name = 'CPython'
         builddate = builddate + ' ' + buildtime
 
-    if hasattr(sys, 'subversion'):
+    if hasattr(sys, '_mercurial'):
+        _, branch, revision = sys._mercurial
+    elif hasattr(sys, 'subversion'):
         # sys.subversion was added in Python 2.5
         _, branch, revision = sys.subversion
     else: