revsets: preserve ordering with the or operator This is valuable because now revsets like 'bookmarks() or tip' will always show tip after bookmarks unless tip was itself a bookmark. This is a somewhat contrived example, but this behavior is useful for "where am I" type aliases that use log and revsets.

--- a/tests/test-revset.t	Wed Apr 13 07:40:24 2011 +0530
+++ b/tests/test-revset.t	Wed Apr 13 12:30:41 2011 -0500
@@ -369,3 +369,8 @@
   hg: parse error at 2: invalid token
   [255]
 
+or operator should preserve ordering:
+  $ log 'reverse(2::4) or tip'
+  4
+  2
+  9