Added messages deprecating the tree and rebuild commands

action/rebuild.go

diff --git a/action/rebuild.go b/action/rebuild.go
index d53b774..83dc301 100644
--- a/action/rebuild.go
+++ b/action/rebuild.go
@@ -18,6 +18,8 @@
 // It remains to be seen whether this is tremendously beneficial to modern Go
 // programs.
 func Rebuild() {
+	msg.Warn("The rebuild command is deprecated and will be removed in a future version")
+	msg.Warn("Use the go install command instead")
 	conf := EnsureConfig()
 	vpath, err := gpath.Vendor()
 	if err != nil {

action/tree.go

diff --git a/action/tree.go b/action/tree.go
index a43a6ba..ce7a917 100644
--- a/action/tree.go
+++ b/action/tree.go
@@ -11,6 +11,7 @@
 
 // Tree prints a tree representing dependencies.
 func Tree(basedir string, showcore bool) {
+	msg.Warn("The tree command is deprecated and will be removed in a future version")
 	buildContext, err := util.GetBuildContext()
 	if err != nil {
 		msg.Die("Failed to get a build context: %s", err)