Changed to clearner solution proposed by @limhoff-r7.

lib/msfenv.rb

@@ -2,11 +2,25 @@
 # Use bundler to load dependencies
 #
 
-gemfile_base = ::File.expand_path(::File.join(::File.dirname(__FILE__), ".."))
-if File.readable?(::File.join(gemfile_base,"Gemfile.local"))
-  ENV['BUNDLE_GEMFILE'] ||= ::File.join(gemfile_base, "Gemfile.local")
-else
-  ENV['BUNDLE_GEMFILE'] ||= ::File.join(gemfile_base, "Gemfile")
+GEMFILE_EXTENSIONS = [
+  '.local',
+  ''
+]
+
+unless ENV['BUNDLE_GEMFILE']
+  require 'pathname'
+
+  msfenv_real_pathname = Pathname.new(__FILE__).realpath
+  root = msfenv_real_pathname.parent.parent
+
+  GEMFILE_EXTENSIONS.each do |extension|
+    extension_pathname = root.join("Gemfile#{extension}")
+
+    if extension_pathname.readable?
+      ENV['BUNDLE_GEMFILE'] = extension_pathname.to_path
+      break
+    end
+  end
 end
 
 begin