gvt restore doesn't work recursively

[shingo-szk]

Hi.

I tried to use gvt restore to resolve dependency recursively, but it doesnt' work.

In source code, downloadDependency tries to read from the copied tree.

gvt/restore.go

Lines 126 to 138 in 50d83ea

	if err := fileutils.Copypath(dst, src, !dep.NoTests, dep.AllFiles); err != nil {
	return err
	}
	if err := fileutils.CopyLicense(dst, wc.Dir()); err != nil {
	return err
	}
	// Check for for manifests in dependencies
	man := filepath.Join(dst, "vendor", "manifest")
	venDir := filepath.Join(dst, "vendor")
	if _, err := os.Stat(man); err == nil {
	m, err := vendor.ReadManifest(man)

But Copypath() seems to ignore manifest because it doesn't look like Go file.

Regards.