moved rails binary to rails gem, so rubygems can find specific versions of rails [#4382 state:resolved]

Signed-off-by: wycats <wycats@gmail.com>

rails.gemspec

@@ -15,8 +15,9 @@ Gem::Specification.new do |s|
   s.homepage          = 'http://www.rubyonrails.org'
   s.rubyforge_project = 'rails'
 
-  s.files = []
-  s.require_path = []
+  s.bindir             = 'bin'
+  s.executables        = ['rails']
+  s.default_executable = 'rails'
 
   s.add_dependency('activesupport',  version)
   s.add_dependency('actionpack',     version)