refs #1681 : modified - sessionvisit table handler when using memcache.

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Conflicts:
	framework/id/textcube/config.default.php
	framework/legacy/Textcube.Control.Session.Memcached.php
 refs #1681 : modified - sessionvisit table handler when using memcache.

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 refs #1681 : added - SessionVisit flush routine.

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Conflicts:
	framework/data/DBModel.php
 refs #1681 : added - SessionVisit flush routine.

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 refs #1681 : bugfix - memcached related bug codes.

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