VbzCart/tables/user tokens

About

 * Purpose: for storing tokens that authorize users to change things associated with an email address (mainly password)
 * History:
 * 2013-10-03 created
 * 2013-12-24 changed to no longer require a pre-existing email address (using SQL adapted for ATC but never used)

SQL
CREATE TABLE `user_tokens` ( `ID`                   INT NOT NULL AUTO_INCREMENT,  `Email`       VARCHAR(256) NOT NULL COMMENT "email address being authorized",  `TokenHash` VARBINARY(128) NOT NULL COMMENT "hash for [token+salt]",  `TokenSalt` VARBINARY(128) NOT NULL COMMENT "random prefix for hash",  `WhenExp`         DATETIME NOT NULL COMMENT "when the token expires (and should be deleted)",   UNIQUE KEY(`Email`),   PRIMARY KEY(`ID`) ) ENGINE = MYISAM;