dev: make the rails version setup more generic

Rakefile

@@ -3,10 +3,7 @@ unless File.exist?('./Gemfile')
 Could not find a Gemfile. Please run any of:
   thor rails:use 3-0-stable
   thor rails:use master
-  thor rails:use 3.0.0
-  thor rails:use 3.0.3
-
-And then run 'bundle install'
+  thor rails:use VERSION (where VERSION is any released version)
 MESSAGE
 end
 require "bundler"

Thorfile

@@ -1,25 +1,15 @@
 class Rails < Thor
-  desc "checkout VERSION", "checks it out"
-  def checkout(version)
-    puts "***** checking out rails at #{version} ..."
-    Dir.chdir("vendor/rails") do
-      `git checkout #{version}`
-      `rm Gemfile.lock` if File.exist?('Gemfile.lock')
-      puts `bundle show`
-    end
-  end
-
-  desc "fetch", "update vendor/rails"
-  def fetch
-    Dir.chdir("vendor/rails") do
-      `git fetch`
-    end
-  end
-
-  desc "use VERSION", "copies the appropriate Gemfile to Gemfile"
+  desc "use VERSION", "configures the Gemfile and runs 'bundle install'"
   def use(version)
-    `cp ./Gemfile-#{version} ./Gemfile` 
-    `rm ./Gemfile.lock`
+    `rm Gemfile.lock` if File.exist?('./Gemfile.lock')
+    `rm Gemfile`      if File.exist?('./Gemfile')
+    case version
+    when /^\d\.\d/
+      `echo 'instance_eval(File.read("./Gemfile-base"))' >> Gemfile`
+      `echo 'gem "rails", "#{version}"' >> Gemfile`
+    else
+      `cp Gemfile-#{version} Gemfile` 
+    end
     system "bundle install"
   end
 end