By default, _redmine_session cookie path is /
This patch sets the path to ENV['RAILS_RELATIVE_URL_ROOT'], so that
multiple instances of redmine have distinct session cookies in any case.
diff -Nur redmine-0.9.0~svn2903/lib/tasks/initializers.rake redmine-0.9.0~svn2903.new/lib/tasks/initializers.rake
--- redmine-0.9.0~svn2903/lib/tasks/initializers.rake	2009-02-21 12:04:50.000000000 +0100
+++ redmine-0.9.0~svn2903.new/lib/tasks/initializers.rake	2009-10-04 23:40:41.963650176 +0200
@@ -17,6 +17,7 @@
 # you'll be exposed to dictionary attacks.
 ActionController::Base.session = {
   :session_key => '_redmine_session',
+  :session_path => ENV['RAILS_RELATIVE_URL_ROOT'].empty? ? '/' : ENV['RAILS_RELATIVE_URL_ROOT'],
   :secret => '#{secret}'
 }
 EOF