made sure `mappend` is used right-associative
made sure `mappend` is used right-associative

bigtable benchmark speedup of > 10%

iblech/blaze-html,dylex/blaze-markup,jgm/blaze-html,FranklinChen/blaze-markup,Soostone/blaze-markup-haste,FranklinChen/blaze-markup,Soostone/blaze-html-haste,Soostone/blaze-markup-haste,jgm/blaze-html,mikehat/blaze-all,mikehat/blaze-all,mikehat/blaze-all,iblech/blaze-html,jgm/blaze-html,dylex/blaze-markup