A fix for --prune.

A fix for --prune.

--- a/mercurial/commands.py	Tue Aug 15 11:47:17 2006 +0200
+++ b/mercurial/commands.py	Tue Aug 15 00:03:48 2006 -0700
@@ -221,7 +221,7 @@
 
     # it might be worthwhile to do this in the iterator if the rev range
     # is descending and the prune args are all within that range
-    for rev in opts.get('prune'):
+    for rev in opts.get('prune', ()):
         rev = repo.changelog.rev(repo.lookup(rev))
         ff = followfilter()
         stop = min(revs[0], revs[-1])