Keep the version hardcoded in mix.exs file

Generated the mix.exs file through configure is not possible when using mix, as
it does not run configure after having downloaded the dependencies.
#621

.gitignore

@@ -41,4 +41,3 @@ XmppAddr.hrl
 /test/*.beam
 /logs/
 /priv/sql
-mix.exs

configure.ac

@@ -235,8 +235,7 @@ esac],[if test "x$lager" = "x"; then lager=true; fi])
 
 AC_CONFIG_FILES([Makefile
 		 vars.config
-		 src/ejabberd.app.src
-		 mix.exs])
+		 src/ejabberd.app.src])
 
 ENABLEUSER=""
 AC_ARG_ENABLE(user,

mix.exs

@@ -3,7 +3,7 @@ defmodule Ejabberd.Mixfile do
 
   def project do
     [app: :ejabberd,
-     version: "@PACKAGE_VERSION@",
+     version: "15.06",
      elixir: "~> 1.0",
      elixirc_paths: ["lib"],
      compile_path: ".",