diff -r c152e538b85b -r b93791e0de25 mercurial/scmutil.py
--- a/mercurial/scmutil.py	Tue Mar 11 16:52:15 2014 -0700
+++ b/mercurial/scmutil.py	Sat Jun 25 02:46:23 2011 +0200
@@ -735,7 +735,9 @@
     if missings:
         raise error.RequirementError(
             _("unknown repository format: requires features '%s' (upgrade "
-              "Mercurial)") % "', '".join(missings))
+              "Mercurial)") % "', '".join(missings),
+            hint=_("see http://mercurial.selenic.com/wiki/MissingRequirement"
+                   " for details"))
     return requirements
 
 class filecachesubentry(object):