Dont set explicit domain for cookies if host is not a domain name

[#6002 state:committed]
Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

When using stylesheet_link_tag(:all) or javascript_include_tag(:all),
assets directories are searched for css or js files. When
config.serve_static_assets is set to true, those files can be
served directly from engine's directories. That's why assets paths
should be set individually for controllers inside engine
if we want to serve static assets with ActionDispatch::Static

class names are already strings, so we do not need to call to_s on the strings that are already strings

Only call save on belongs_to associations if the record has changed or any nested associations have changed (resolves #3353)
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Includes test and documentation for new feature
Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>