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/recurring_todos/abstract_recurrence_pattern.rb

@@ -151,7 +151,7 @@ module RecurringTodos
     end
 
     def get_next_date(previous)
-      raise "Should not call AbstractRecurrencePattern.get_next_date directly. Overwrite in subclass"
+      raise "Should not call AbstractRecurrencePattern.get_next_date directly. Override in subclass"
     end
 
     def continues_recurring?(previous)
@@ -174,13 +174,13 @@ module RecurringTodos
     # same day as the previous
     def determine_start(previous, offset=0.day)
       start = self.start_from || NullTime.new
-      now = Time.zone.now
       if previous
         # check if the start_from date is later than previous. If so, use
         # start_from as start to search for next date
         start > previous ? start : previous + offset
       else
         # skip to present
+        now = Time.zone.now
         start > now ? start : now
       end
     end
@@ -199,32 +199,24 @@ module RecurringTodos
     end
 
     def find_last_day_x_of_month(weekday, month, year)
-      # count backwards. use UTC to avoid strange timezone oddities
-      # where last_day -= 1.day seems to shift tz+0100 to tz+0000
-      last_day = Time.utc(year, month, Time.days_in_month(month))
+      last_day = Time.zone.local(year, month, Time.days_in_month(month))
       while last_day.wday != weekday
         last_day -= 1.day
       end
-      # convert back to local timezone
-      Time.zone.local(last_day.year, last_day.month, last_day.day)
+      last_day
     end
 
     def find_xth_day_of_month(x, weekday, month, year)
-      # 1-4th -> count upwards last -> count backwards. use UTC to avoid strange
-      # timezone oddities where last_day -= 1.day seems to shift tz+0100 to
-      # tz+0000
-      start = Time.utc(year,month,1)
+      start = Time.zone.local(year,month,1)
       n = x
       while n > 0
         while start.wday() != weekday
-          start+= 1.day
+          start += 1.day
         end
         n -= 1
-        start+= 1.day unless n==0
+        start += 1.day unless n==0
       end
-      # convert back to local timezone
-      Time.zone.local(start.year, start.month, start.day)
+      start
     end
-
   end
 end