cat: fix cat without -r, broken by 0ae35296fbf4
The default revision for revsingle() is now '.' instead of None. This
preserves the behavior of cat prior to it using revsingle().
--- a/mercurial/cmdutil.py Thu Oct 07 18:24:29 2010 -0500
+++ b/mercurial/cmdutil.py Fri Oct 08 14:02:23 2010 -0500
@@ -111,7 +111,7 @@
limit = None
return limit
-def revsingle(repo, revspec, default=None):
+def revsingle(repo, revspec, default='.'):
if not revspec:
return repo[default]