cleanup: "x != None" -> "x is not None"

cleanup: "x != None" -> "x is not None"

--- a/tests/hghave	Sat May 12 15:54:54 2012 +0200
+++ b/tests/hghave	Sat May 12 15:56:23 2012 +0200
@@ -31,14 +31,14 @@
 def has_bzr():
     try:
         import bzrlib
-        return bzrlib.__doc__ != None
+        return bzrlib.__doc__ is not None
     except ImportError:
         return False
 
 def has_bzr114():
     try:
         import bzrlib
-        return (bzrlib.__doc__ != None
+        return (bzrlib.__doc__ is not None
                 and bzrlib.version_info[:2] >= (1, 14))
     except ImportError:
         return False