exp/norm: generate trie struct in triegen.go for better encapsulation.
exp/norm: generate trie struct in triegen.go for better encapsulation.

R=r, r
CC=golang-dev
http://codereview.appspot.com/4837071
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go