added "a2enmod include" for ssi to the doc

redray

2008-12-15 1f0c31efc4cf2c438ffd75960140ddb66b0fe042

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auth    required   pam_mysql.so user={mysql_server_ispconfig_user} passwd={mysql_server_ispconfig_password} host={mysql_server_ip} db={mysql_server_database} table=mail_user usercolumn=email passwdcolumn=password crypt=1
account sufficient pam_mysql.so user={mysql_server_ispconfig_user} passwd={mysql_server_ispconfig_password} host={mysql_server_ip} db={mysql_server_database} table=mail_user usercolumn=email passwdcolumn=password crypt=1