Ruby1.9: skip enforcing UTF-8 encodings on the params hash on Rails2 if it is frozen...

Ruby1.9: skip enforcing UTF-8 encodings on the params hash on Rails2 if it is frozen (#4050, #4796)

Tests on CI server fail.
http://www.redmine.org/builds/build_trunk-1.9.2-sqlite3_257.html

<pre>
  1) Error:
test_index_with_short_filters(IssuesControllerTest):
RuntimeError: can't modify frozen string
    /var/lib/hudson/jobs/trunk-1.9.2-sqlite3/workspace/app/controllers/application_controller.rb:58:in `force_encoding'
    /var/lib/hudson/jobs/trunk-1.9.2-sqlite3/workspace/app/controllers/application_controller.rb:58:in `utf8nize!'
    /var/lib/hudson/jobs/trunk-1.9.2-sqlite3/workspace/app/controllers/application_controller.rb:60:in `block in utf8nize!'
    /var/lib/hudson/jobs/trunk-1.9.2-sqlite3/workspace/app/controllers/application_controller.rb:60:in `each'
    /var/lib/hudson/jobs/trunk-1.9.2-sqlite3/workspace/app/controllers/application_controller.rb:60:in `utf8nize!'
    /var/lib/hudson/jobs/trunk-1.9.2-sqlite3/workspace/app/controllers/application_controller.rb:52:in `params_filter'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/activesupport-2.3.14/lib/active_support/callbacks.rb:178:in `evaluate_method'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/activesupport-2.3.14/lib/active_support/callbacks.rb:166:in `call'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/actionpack-2.3.14/lib/action_controller/filters.rb:225:in `call'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/actionpack-2.3.14/lib/action_controller/filters.rb:629:in `run_before_filters'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/actionpack-2.3.14/lib/action_controller/filters.rb:615:in `call_filters'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/actionpack-2.3.14/lib/action_controller/filters.rb:610:in `perform_action_with_filters'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/actionpack-2.3.14/lib/action_controller/benchmarking.rb:68:in `block in perform_action_with_benchmark'
    /var/lib/hudson/ruby1.9.2/lib/ruby/gems/1.9.1/gems/activesupport-2.3.14/lib/active_support/core_ext/benchmark.rb:17:in `block in ms'
</pre>

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@8716 e93f8b46-1217-0410-a6f0-8f06a7374b81