2014-01-22: merge stable into default.

merge stable into default.

diff --git a/.hgtags b/.hgtags
--- a/.hgtags
+++ b/.hgtags
@@ -12,3 +12,4 @@ 3f72f85e4cddf57e5e6c84c735f554f330d3b88b
 2ae2c7c154e0c80acd21bdb2dace1c98a0a8d7a7 v0.5.6
 fb1b0fb41bc768485f582f3f5af16478aa6212a1 v0.5.7
 efd0ee6e65c3948e0c643526063029b691424de8 v0.5.8
+bb1c4165b8a6d12929625e6518a5b1c727c75942 v0.5.9