Restore forced If-Modified-Since for intra-site thread watcher requests.

src/Monitoring/ThreadStats.coffee

@@ -77,6 +77,7 @@ ThreadStats =
     ThreadStats.timeout = setTimeout ThreadStats.fetchPage, 2 * $.MINUTE
     $.ajax "#{location.protocol}//a.4cdn.org/#{ThreadStats.thread.board}/threads.json", onload: ThreadStats.onThreadsLoad,
       whenModified: 'ThreadStats'
+      bypassCache:  true
 
   onThreadsLoad: ->
     if @status is 200

src/Monitoring/ThreadUpdater.coffee

@@ -236,6 +236,7 @@ ThreadUpdater =
       timeout:   $.MINUTE
     ,
       whenModified: 'ThreadUpdater'
+      bypassCache:  true
 
   updateThreadStatus: (type, status) ->
     return if not (hasChanged = ThreadUpdater.thread["is#{type}"] isnt status)

src/Monitoring/ThreadWatcher.coffee

@@ -224,6 +224,8 @@ ThreadWatcher =
         onloadend: ->
           ThreadWatcher.parseStatus.call @, thread
         timeout: $.MINUTE
+      ,
+        whenModified: if force then false else 'ThreadWatcher'
     else
       req = {abort: () -> req.aborted = true}
       CrossOrigin.json url, ->

src/platform/$.coffee

@@ -51,7 +51,7 @@ $.ajax = do ->
     pageXHR = XMLHttpRequest
 
   (url, options={}, extra={}) ->
-    {type, whenModified, upCallbacks, form} = extra
+    {type, whenModified, bypassCache, upCallbacks, form} = extra
     options.responseType ?= 'json' if /\.json$/.test url
     # XXX https://forums.lanik.us/viewtopic.php?f=64&t=24173&p=78310
     url = url.replace /^((?:https?:)?\/\/(?:\w+\.)?4c(?:ha|d)n\.org)\/adv\//, '$1//adv/'
@@ -59,7 +59,7 @@ $.ajax = do ->
       params = []
       # XXX https://bugs.chromium.org/p/chromium/issues/detail?id=643659
       params.push "s=#{whenModified}" if $.engine is 'blink'
-      params.push "t=#{Date.now()}" if Site.software is 'yotsuba'
+      params.push "t=#{Date.now()}" if Site.software is 'yotsuba' and bypassCache
       url0 = url
       url += '?' + params.join('&') if params.length
     r = new pageXHR()