This fixes failing tests when the timezone is different than utc

There were several problems:
* Time.now returns the systems time, not the users time
* fixtures do not translate dates from timezone to utc, but stores the
  date verbatim
* calling a controller will set the timezone to the preference of the
  current_user. So it could be changed while you do not realize this. I
  fixed the failing test, but problems could be elsewhere

app/models/stats/totals.rb

@@ -19,7 +19,7 @@ module Stats
     end
 
     def first_action_at
-      first_action.created_at if first_action
+      first_action.try(:created_at)
     end
 
     def projects