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=40511178770ab197b8c12d2cc57b5bfbf30af3f4
http://github.com/moodle/moodle/commit/40511178770ab197b8c12d2cc57b5bfbf30af3f4
+ 3.8 en [modeloutputdirwithdefaultinfo,core_analytics]