Get ejabberd version from vars.config

mix.exs

@@ -3,7 +3,7 @@ defmodule Ejabberd.Mixfile do
 
   def project do
     [app: :ejabberd,
-     version: "21.4.0",
+     version: version(),
      description: description(),
      elixir: "~> 1.4",
      elixirc_paths: ["lib"],
@@ -17,6 +17,14 @@ defmodule Ejabberd.Mixfile do
      deps: deps()]
   end
 
+  def version do
+    case config(:vsn) do
+      :false -> "0.0.0" # ./configure wasn't run: vars.config not created
+      '0.0' -> "0.0.0" # the full git repository wasn't downloaded
+      vsn -> String.replace(:erlang.list_to_binary(vsn), ".0", ".")
+    end
+  end
+
   def description do
     """
     Robust, Ubiquitous and Massively Scalable Messaging Platform (XMPP, MQTT, SIP Server)