refs #1633 : implement - added customizable trash keeping period
 - $service['trashtimelimit'] determines keeping period of trash
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 - Default value is 3.5 days. (originally it was 15 days without any
	 option)
 - Checking interval is changed from 86400sec. to 43200sec.
 - Codebase of function trashVan() is changed from 1.7/8 to 2.0 codebase.