Added an active field track if an Enumeration is active on the frontend view.

* Changed TimelogHelper#activity_collection_for_select_options to only use
  active TimeEntryActivities.
* Changed TimelogHelper#activity_collection_for_select_options to return a blank
  option if the time_entry's current activity is inactive.

  #4077

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2946 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20090401231134_add_active_field_to_enumerations.rb

@@ -0,0 +1,9 @@
+class AddActiveFieldToEnumerations < ActiveRecord::Migration
+  def self.up
+    add_column :enumerations, :active, :boolean, :default => true, :null => false
+  end
+
+  def self.down
+    remove_column :enumerations, :active
+  end
+end