Correctly override image_path in sprockets rails_helper

Avoid use of existing precompiled assets during rake assets:precompile run

Fix: habtm doesn't respect select query method

Give precedence to `config.digest = false` over the existence of manifest.yml asset digests

Closes #3104.

Previously, it would use send() to get the attribute. In Active
Resource, this would rely on hitting method missing. If a method with
the same name was defined further up the ancestor chain, that method
would wrongly be called.

This change fixes test_to_xml_with_private_method_name_as_attribute in
activeresource/test/cases/base_test.rb, which was broken after
51bef9d8, because that change made
to_xml use serializable_hash.

CollectionProxy#replace should change the DB records rather than just mutating the array. Fixes #3020.

The options argument to MessageVerifier#initialize should be a hash.

Implement Mime::Type#respond_to? (consistently with #method_missing) Closes #3032

escape options for the stylesheet_link_tag method

Public API for add new compressors to Sprockets

remove superfluous to_s in ERB::Util.html_escape

Re-launch assets:precompile task using (Rake.)ruby instead of Kernel.exec so it works on Windows

This reverts commit 0e4748cd.

To the app developer, this means configuration add in
config/initializers/* will not be executed.

Plugins developers need to special case their initializers that are
meant to be run in the assets group by adding :group => :assets.

Conflicts:

	railties/CHANGELOG
	railties/test/application/assets_test.rb

Remove Sprockets compute_public_path, AV compute_plubic_path can be used 

Minor doc fix to String#constantize

Sprockets to use config.assets.prefix, with tests

Added ActiveSupport::Inflector.safe_constantize and String#safe_constantize; refactored common constantize tests into ConstantizeTestCases