Use rubigen as framework for rails_generator

RubiGen (http://rubigen.rubyforge.org) was an extraction of rails_generator to provide an awesome generator mechanism for any framework, not just Rails. It was created in 2007, and presented at RubyConf 2007 (http://rubyconf2007.confreaks.co...

Jeremy Kemper asked for it to patched back into Rails. This ticket is for that patch request.

The patch is found in the branch http://github.com/drnic/rails/tr... (built off edge rails from 27/12/2008)

All generator-related tests are passing.

The following sample usage demonstrates it working via the "rails" and "script/generate" commands:

git clone git://github.com/drnic/rubigen.git
cd rubigen
rake install_gem
cd ..
git clone git://github.com/drnic/rails.git 
cd rails
git checkout -b merge_rubigen --track
gl origin merge_rubigen
ruby railties/bin/rails test_app
cd test_app
ln -s ../.. vendor/rails
script/generate model Person name:string
script/generate model
script/generate

The two last commands will show the discovery mechanism of generators as per the current rails mechanism (gems, plugins, ~/.rails/generators, lib/generators, etc)

This patch also includes the inclusion of "script/update" in the rails app scaffold. I personally don't get the point of it, and in 4 years have never wondered why it was never included. But there is "rails_generator/scripts/update.rb" code, so I figure at some stage someone thought it was a good idea.

If script/update is a bad idea, then let's remove all references to it.

I have not frozen rubigen into the rails source yet, though the vendor.rb place for it is ready. This ticket may spark some discussion about rubigen/rails_generator leading to some refactorings prior the inclusion of this patch/branch into edge rails.