A patch for cooking escaping bug

Hi,

I think I found a bug in cookie escaping.  RestClient was unescaping cookie string to send out instead of escaping.

I had an issue when I was passing Rack session between internal servers and the cookie was truncated.  With this patch, it worked on my environment.

I've attached a test case, but I am new to RSpec.  I've mimiced the similar spec, but might contain unnecessary code.