#1675 (ok 4.5) Add support for INET6_ATON and INET6_NTOA

[Tom Sommer]

This function was added in MySQL 5.6.3.

http://dev.mysql.com/doc/refman/5.6/en/miscellaneous-functions.html

[Isaac Bennetch]

Implemented with https://github.com/phpmyadmin/phpmyadmin/commit/76349057620b68eb5b079d76acde5e8d78c369bc