'gb generate' fails on subdirectories of 'cmd'

[ldm5180]

This is basically a reopening of #492

When there is a subdirectory/sub-package of src/cmd, it fails to build with an error that looks like this:

--- FAIL: TestGbBuildSubPackageOfCmd (0.06s)
    gb_test.go:179: running /tmp/testgb347664536/testgb [generate]
    gb_test.go:193: standard error:
    gb_test.go:194: can't load package: package cmd/hello: open /usr/lib/go/src/cmd/hello: no such file or directory
        FATAL: command "generate" failed: exit status 1

    gb_test.go:203: gb [generate] failed unexpectedly: exit status 1

It appears that the search path does not contain both the $GB_PROJECT_DIR and the $GB_GOROOT. It only contains the $GB_GOROOT.

I will shortly contribute a pull request which causes TestGbBuildSubPackageOfCmd to fail.

[ldm5180]

Opened new issue #565

[davecheney]

I think this is a limitation of go generate, gb is constructing an appropriate GOPATH, but go generate uses the go/build package which has the limitation of assuming anything matching ^cmd/ lives in GOROOT.

solution: namespace your package appropriately, $PROJECT/src/github.com/ldm5180/