safehasattr: new function to work around hasattr being broken

safehasattr: new function to work around hasattr being broken

--- a/mercurial/util.py	Mon Jul 25 16:14:02 2011 -0500
+++ b/mercurial/util.py	Mon Jul 25 14:59:55 2011 -0500
@@ -75,6 +75,10 @@
 def sha1(s):
     return _fastsha1(s)
 
+_notset = object()
+def safehasattr(thing, attr):
+    return getattr(thing, attr, _notset) is not _notset
+
 def _fastsha1(s):
     # This function will import sha1 from hashlib or sha (whichever is
     # available) and overwrite itself with it on the first call.