db: Translate abbreviations like 'CDT'

include/class.timezone.php

@@ -166,7 +166,15 @@ class DbTimezone {
         // Attempt to fetch timezone direct from the database
         $TZ = db_timezone();
 
-        // SYSTEM does not describe a time zone
+        // Forbid timezone abbreviations like 'CDT'
+        if (!in_array($TZ, array('UTC', 'GMT')) && strpos($TZ, '/') === false)
+            // Attempt to lookup based on the abbreviation
+            if (!($TZ = timezone_name_from_abbr($TZ)))
+                // Abbreviation doesn't point to anything valid
+                return false;
+
+        // SYSTEM does not describe a time zone, ensure we have a valid zone
+        // by attempting to create an instance of DateTimeZone()
         try {
             new DateTimeZone($TZ);
             return $TZ;