(dev/core#174) System::flushCache() - Continue existing behavior afte…

…ring fixing prefixes

The preceding update to `CRM_Utils_Cache` meant that `CRM_Utils_Cache::singleton()->flush()`
(aka `Civi::cache()->flush()`) would flush only the *default* cache. This revision
ensures that a general system-flush still hits the same caches.

However, we can now define *other* caches which *won't* be hit by system-flush.

CRM/Utils/System.php

@@ -1416,8 +1416,12 @@ public static function civiExit($status = 0) {
   public static function flushCache() {
     // flush out all cache entries so we can reload new data
     // a bit aggressive, but livable for now
-    $cache = CRM_Utils_Cache::singleton();
-    $cache->flush();
+    Civi::cache()->flush();
+    Civi::cache('settings')->flush();
+    Civi::cache('js_strings')->flush();
+    Civi::cache('community_messages')->flush();
+    CRM_Extension_System::singleton()->getCache()->flush();
+    CRM_Cxn_CiviCxnHttp::singleton()->getCache()->flush();
 
     // also reset the various static memory caches