Don't try to clone vundle if we already have it [Fix #415]

Rakefile

@@ -91,21 +91,19 @@ end
 desc "Runs Vundle installer in a clean vim environment"
 task :install_vundle do
   puts "======================================================"
-  puts "Installing vundle."
+  puts "Installing and updating vundles."
   puts "The installer will now proceed to run BundleInstall."
-  puts "Due to a bug, the installer may report some errors"
-  puts "when installing the plugin 'syntastic'. Fortunately"
-  puts "Syntastic will install and work properly despite the"
-  puts "errors so please just ignore them and let's hope for"
-  puts "an update that fixes the problem!"
   puts "======================================================"
 
   puts ""
 
-  run %{
-    cd $HOME/.yadr
-    git clone https://github.com/gmarik/vundle.git #{File.join('vim','bundle', 'vundle')}
-  }
+  vundle_path = File.join('vim','bundle', 'vundle')
+  unless File.exists?(vundle_path)
+    run %{
+      cd $HOME/.yadr
+      git clone https://github.com/gmarik/vundle.git #{vundle_path}
+    }
+  end
 
   Vundle::update_vundle
 end