Revert "The rails gem doesn't have a lib directory - closes #1958."

RubyGems requires at least one require_path.

This reverts commit e7fc5d1cad.

rails.gemspec

@@ -14,9 +14,8 @@ Gem::Specification.new do |s|
   s.email             = 'david@loudthinking.com'
   s.homepage          = 'http://www.rubyonrails.org'
 
-  s.bindir            = 'bin'
-  s.executables       = ['rails']
-  s.require_paths     = []
+  s.bindir             = 'bin'
+  s.executables        = ['rails']
 
   s.add_dependency('activesupport',  version)
   s.add_dependency('actionpack',     version)