2014-01-22: merge release into default.

merge release into default.

diff --git a/.hgtags b/.hgtags
--- a/.hgtags
+++ b/.hgtags
@@ -9,3 +9,4 @@ 00de78a95055f846906d57b1a094a1c3e6bb2dbd
 df64e82e0920bdd079d77cd4829bac9d30461a25 v0.5.3
 f9c6e637d91d107bbf2ad807f30dc04150ddb251 v0.5.4
 3f72f85e4cddf57e5e6c84c735f554f330d3b88b v0.5.5
+2ae2c7c154e0c80acd21bdb2dace1c98a0a8d7a7 v0.5.6