It seems that the new mysqli library is the future for mysql access. So we have to extend XMLDB and Moodle support for this:
1) XMLDB must support the driver.
2) Every ocurrence of 'mysql' across code, must be completed with the corresponding 'mysqli'
Note: 2) Can be replaced by the concept of $CFG->dbfamily, as especified in
MDL-7061 (need decision)