Fixing Plugin and Mailer default_url_options.

Fixing Plugin and Mailer default_url_options.

Both the plugin hooks and Mailer were setting default_url_options incorrectly
and causing ActionContoller::UrlWritter to cache the settings on the module
(mattr_accessor) causing several url generators to fail in either the plugin
hooks or the Mailer.

* Replaced Mailer's use of the default_url_options accessor with the proper class method
* Replaced Hook's use of the default_url_options accessor with the proper class method on the ViewListener class
* Added a test to reproduce the bugs in the Mailer when a hook is registered (thanks Chaoqun Zou)

  #2542

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2522 e93f8b46-1217-0410-a6f0-8f06a7374b81