Git commits in Moodle 3.1.12 by Tim Hunt

commit b7bbe9fd9466036a84fe7bc4619b376f05b7049f
Author: Tim Hunt <T.J.Hunt@open.ac.uk>
Date:   Tue, 01 May 2018 02:45:47 +0800
Tag:    v3.1.12

MDL-62275 qtype_calc*: improve validation of formulae