Railties RDocs task fails with wrong constant name

Currently the Railties RDoc task fails with "wrong constant name ../DOC/TEMPLATE/HORO". This seems to be caused by the load_paths require at the top of the Rakefile. Removing the line doesn't seem to have any effect - all tests still run and pass. The attached patch removes this line and also cleans up the included files for RDoc to process as commands and generators are now inside lib/rails and there are no vendor items any longer.