Fixed #10006 -- Avoid inadvertently using third-party "json" module.

In r9707 we added a preference to use Python's standard json module (Python 2.6
and beyond). However, there is also a third-party module called json that was
being picked up by accident if it was installed. It isn't API compatible, so
bad things happened. This change avoids that problem.

Patch from markmuetz.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9910 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/utils/simplejson/__init__.py

@@ -119,8 +119,14 @@ except ImportError:
 if not use_system_version:
     try:
         from json import *      # Python 2.6 preferred over local copy.
+
+        # There is a "json" package around that is not Python's "json", so we
+        # check for something that is only in the namespace of the version we
+        # want.
+        JSONDecoder
+
         use_system_version = True
-    except ImportError:
+    except (ImportError, NameError):
         pass
 
 # If all else fails, we have a bundled version that can be used.