go.tools/dashboard/app: fix tests and add TODO to reall fix them
go.tools/dashboard/app: fix tests and add TODO to reall fix them

This change is a really nasty hack to preserve the magic header
across requests. The nasty hack will go away once we refactor these
tests to use the new "appengine/aetest" package instead.

R=golang-dev, dvyukov
CC=golang-dev
https://codereview.appspot.com/39230043

d0f/go-zh.tools,8limbs/gotools,bryanxu/go-zh.tools,bryanxu/go-zh.tools,bryanxu/go-zh.tools,skyportsystems/go.tools,webfd/go-zh.tools,d0f/go-zh.tools,skyportsystems/go.tools,webfd/go-zh.tools,8limbs/gotools,webfd/go-zh.tools,skyportsystems/go.tools,webfd/go-zh.tools,d0f/go-zh.tools,skyportsystems/go.tools,d0f/go-zh.tools,d0f/go-zh.tools,bryanxu/go-zh.tools,webfd/go-zh.tools,bryanxu/go-zh.tools,skyportsystems/go.tools,8limbs/gotools