title: devise registration confirmation freezes when I click email confirm link
body: <p>I'm getting some strange behavior when testing on my local machine:</p>
  
  <p>1) First of all when I sign-up, I'm redirected to the home page and I see a flash message that says:</p>
  
  <pre><code> "You have signed up successfully. However, we could not sign you in because your account is unconfirmed."
  </code></pre>
  
  <p>I find it strange to see a warning type message when the user is merely on the right path to creating an account.  I could easily change the message in /locales/devise.en.yml, but I just wanted to confirm this was the default behavior of devise, and not something wrong with my setup?</p>
  
  <p>2) I successfully receive an email with a confirmation link:</p>
  
  <pre><code>&lt;p&gt;You can confirm your account through the link below:&lt;/p&gt;
  
  &lt;p&gt;&lt;a href="http://localhost:5000/accounts/confirmation?confirmation_token=MywxHuW3PWHvg6x2nUfG&amp;amp;format="&gt;Confirm my account&lt;/a&gt;&lt;/p&gt;
  </code></pre>
  
  <p>When I click on the email confirmation link, I see a blank web page.</p>
  
  <p>the development log shows:</p>
  
  <pre><code>Started GET "/accounts/confirmation?confirmation_token=MywxHuW3PWHvg6x2nUfG&amp;format=" for   127.0.0.1 at 2011-09-28 09:41:55 -0700
     Processing by Devise::ConfirmationsController#show as 
    Parameters: {"confirmation_token"=&gt;"MywxHuW3PWHvg6x2nUfG"}
    SQL (0.9ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
   FROM pg_attribute a LEFT JOIN pg_attrdef d
   ON a.attrelid = d.adrelid AND a.attnum = d.adnum
   WHERE a.attrelid = '"artists"'::regclass
   AND a.attnum &gt; 0 AND NOT a.attisdropped
   ORDER BY a.attnum
    Artist Load (0.4ms)  SELECT "artists".* FROM "artists" WHERE   "artists"."confirmation_token" = 'MywxHuW3PWHvg6x2nUfG' LIMIT 1
    SQL (0.8ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
    FROM pg_attribute a LEFT JOIN pg_attrdef d
    ON a.attrelid = d.adrelid AND a.attnum = d.adnum
    WHERE a.attrelid = '"artists"'::regclass
    AND a.attnum &gt; 0 AND NOT a.attisdropped
    ORDER BY a.attnum
     SQL (0.2ms)  BEGIN
     AREL (0.9ms)  UPDATE "artists" SET "confirmation_token" = NULL, "confirmed_at" = '2011-09-28 16:41:55.894603', "updated_at" = '2011-09-28 16:41:55.895467' WHERE "artists"."id" = 85
    [paperclip] Saving attachments.
    SQL (0.8ms)  COMMIT
    SQL (0.1ms)  BEGIN
    AREL (0.5ms)  UPDATE "artists" SET "last_sign_in_at" = '2011-09-28 16:41:55.915779', "current_sign_in_at" = '2011-09-28 16:41:55.915779', "last_sign_in_ip" = '127.0.0.1', "current_sign_in_ip" = '127.0.0.1', "sign_in_count" = 1, "updated_at" = '2011-09-28  16:41:55.916532' WHERE "artists"."id" = 85
     [paperclip] Saving attachments.
    SQL (0.5ms)  COMMIT
    Completed 406 Not Acceptable in 231ms
  </code></pre>
  
  <p>"Not Acceptable" it says?  What does that mean?  Did it go through or not?  What happened?</p>