Fix extremely slow auto-update of ancient timestamps

When a timestamp is several months old, and we leave
the application around (in a forgotten tab) for
more than three weeks, the usual method of updating
the timestamp fails.

This change works around that by maxing out our timeouts
at 24 days. (This will simply cause us to check the
time in every 24 days.)

Fixes #1952.

I also moved the 5-second minimum to the same time helper.

h/static/scripts/directives/annotation.coffee

@@ -237,7 +237,6 @@ AnnotationController = [
     updateTimestamp = (repeat=false) =>
       @timestamp = timeHelpers.toFuzzyString model.updated
       fuzzyUpdate = timeHelpers.nextFuzzyUpdate model.updated
-      fuzzyUpdate = 5 if fuzzyUpdate < 5  # minimum 5 seconds
       nextUpdate = (1000 * fuzzyUpdate) + 500
       return unless repeat
       $timeout =>

h/static/scripts/helpers/time-helpers.coffee

@@ -49,7 +49,15 @@ createTimeHelpers = ->
     return null if not date
     {_, breakpoint} = getBreakpoint(date)
     return null unless breakpoint
-    return breakpoint[2]
+    secs = breakpoint[2]
+
+    # We don't want to refresh anything more often than 5 seconds
+    secs = Math.max secs, 5
+
+    # setTimeout limit is MAX_INT32=(2^31-1) (in ms),
+    # which is about 24.8 days. So we don't set up any timeouts
+    # longer than 24 days, that is, 2073600 seconds.
+    secs = Math.min secs, 2073600
 
 angular.module('h.helpers')
 .factory('timeHelpers', createTimeHelpers)