Projects without a mix.exs can't be recursive

Otherwise, recursive_enabled? always returns true, even
when it should be disabled, affecting the output of tasks.

Closes #1374

Author: José Valim

lib/mix/lib/mix/server.ex

@@ -85,7 +85,7 @@ defmodule Mix.Server do
       [ Project[rec_enabled?: bool] | _ ] ->
         { :reply, bool, config }
       _ ->
-        { :reply, true, config }
+        { :reply, false, config }
     end
   end
 

lib/mix/test/mix/tasks/compile_test.exs

@@ -39,6 +39,13 @@ defmodule Mix.Tasks.CompileTest do
     Mix.Project.pop
   end
 
+  test "compile is no-op on empty project" do
+    in_fixture "beams", fn ->
+      Mix.Tasks.Compile.run []
+      refute File.exists?("ebin")
+    end
+  end
+
   test "compile a project without mixfile" do
     in_fixture "no_mixfile", fn ->
       Mix.Tasks.Compile.run []