Remove "circular require considered harmful" error

rails/generators should not load rails/generators/base since the
latter is loading it.
More Warnings removed for ruby trunk

Same as 4d4ff531b8807ee88a3fc46875c7e76f613956fb
shadowing variable warning removed
Set the destination_root for plugins

Since the plugin generator is relying on the application one, we need to
define the proper root when creating the plugin. The AppBase class is
not setting the destination_root (this is done via the AppGenerator)
Fix some failing tests for Rails::Paths

Since we are not using the File.exists? alias which raises a warning on
current ruby trunk, few stubs are wrong.
Use consistent order of the arguments
:bomb:
Fix typo in method description in Responder class

Fixes a typo in the description for the call class method in Responder.
Merge pull request #12728 from arunagw/aa-warnings-removed-ruby-trunk

More Warnings removed for ruby trunk
Merge pull request #12735 from linstula/fix-typo-in-responder-comment

Fix typo in method description in Responder class
Merge pull request #12733 from robin850/fix-railties-build

Fix railties build