"veyron/tools/principal": Part 4: seekblessings

Add support for the "seekblessings" command to the principal
tool. The command expects the Veyron Identity Server to provide
a security.WireBlessings (as opposed to a serialzied PublicID)
in exchange for a Macaroon obtained from the OAuth flow described
in:

https://docs.google.com/a/google.com/document/d/1SRoc2cKE9iE1fWR7aSmMoccZoi4ZE8BQL7sr1LDNVkk/edit

Change-Id: I200caa7807531ea5cc21ac534879a7c39927f6a1
diff --git a/tools/principal/main_nacl.go b/tools/principal/main_nacl.go
new file mode 100644
index 0000000..9dea3b5
--- /dev/null
+++ b/tools/principal/main_nacl.go
@@ -0,0 +1,3 @@
+package main
+
+const openCommand = ""