revsingle: fix silly API issue (issue2992) stable

revsingle: fix silly API issue (issue2992)

--- a/mercurial/scmutil.py	Fri Jul 26 15:05:48 2013 -0500
+++ b/mercurial/scmutil.py	Fri Jul 26 15:42:10 2013 -0500
@@ -556,7 +556,7 @@
     return _rcpath
 
 def revsingle(repo, revspec, default='.'):
-    if not revspec:
+    if not revspec and revspec != 0:
         return repo[default]
 
     l = revrange(repo, [revspec])