Author: Paul Holden
MDL-66392 analytics: make model output directory default to empty.
Falling back to path within $CFG->dataroot/models.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=cecd90ffecb6ac228a71a7cfe6c930b674dd2643
http://github.com/moodle/moodle/commit/cecd90ffecb6ac228a71a7cfe6c930b674dd2643
+ 4.0 en [modeloutputdirwithdefaultinfo,core_analytics]