Godep is the tool to manage dependency of go. It solves the problem that seagull possibly doesn't work if the dependent Beego has updated.
Here is the Github page of godep, https://github.com/tools/godep.
There's an example of usage and you can go to http://www.goinggo.net/2013/10/manage-dependencies-with-godep.html.
Have you noticed the folder named Godeps? It's generated by godep and contains all the source code of my go dependency.
We simply run godep save and the current Beego project is downloaded in Godeps.
It makes sure that the current version of Beego is stable and it always works with godep go build.
Normally go get and go build works like a charm but we use godep for stability.