* 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