Added Redmine::Plugin::Hook::Manager.clear_listeners to remove all hook listeners.

lib/redmine/plugin.rb

@@ -192,6 +192,13 @@ module Redmine #:nodoc:
             end
           end
 
+          # Removes all listeners
+          def clear_listeners()
+            @@hooks.each do |hook, registrations|
+              @@hooks[hook] = []
+            end
+          end
+        
           # Run all the hooks for +hook_name+ passing in +context+
           def call_hook(hook_name, context = { })
             response = ''