In Go it's much more efficient to build several commands in the same
`go build` because the build has to load most of the dependency tree
each time. Roughly 50% on my machine:
Together (go1.2 on OS X):
real 0m4.049s
user 0m8.387s
sys 0m2.766s
Separate:
real 0m13.392s
user 0m12.420s
sys 0m6.882s