Revert "After three long, hard years... we know how to upgrade"

This reverts commit f6f5ea1b.

paperclip.gemspec

@@ -17,6 +17,10 @@ Gem::Specification.new do |s|
   s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
   s.require_paths = ["lib"]
 
+  if File.exists?('UPGRADING')
+    s.post_install_message = File.read("UPGRADING")
+  end
+
   s.requirements << "ImageMagick"
   s.required_ruby_version = ">= 1.9.2"