Always prompt once for sudo

lib/bundler.rb

@@ -329,17 +329,23 @@ def which(executable)
     def sudo(str)
       SUDO_MUTEX.synchronize do
         prompt = "\n\n" + <<-PROMPT.gsub(/^ {6}/, "").strip + " "
-        Your user account isn't allowed to install to the system Rubygems.
+        Your user account isn't allowed to install to the system RubyGems.
         You can cancel this installation and run:
 
             bundle install --path vendor/bundle
 
         to install the gems into ./vendor/bundle/, or you can enter your password
-        and install the bundled gems to Rubygems using sudo.
+        and install the bundled gems to RubyGems using sudo.
 
         Password:
         PROMPT
 
+        unless @prompted_for_sudo ||= system(%(sudo -k -p "#{prompt}" true))
+          raise SudoNotPermittedError,
+            "Bundler requires sudo access to install at the moment. " \
+            "Try installing again, granting Bundler sudo access when prompted, or installing into a different path."
+        end
+
         `sudo -p "#{prompt}" #{str}`
       end
     end

lib/bundler/errors.rb

@@ -52,6 +52,7 @@ class LockfileError < BundlerError; status_code(20); end
   class CyclicDependencyError < BundlerError; status_code(21); end
   class GemfileLockNotFound < BundlerError; status_code(22); end
   class PluginError < BundlerError; status_code(29); end
+  class SudoNotPermittedError < BundlerError; status_code(30); end
   class GemfileEvalError < GemfileError; end
   class MarshalError < StandardError; end