Git commits in Moodle 2.7.18 by David Mudrák

commit d88aa76c773170e8c396d767c00245d07d2c0e0d
Author: David Mudrák <david@moodle.com>
Date:   Thu, 05 Jan 2017 20:20:59 +0800
Tag:    v2.7.18

MDL-57580 mod_assign: Fix the incorrect type of some input parameters


commit a444a47d14e8a8209d1fc718eacec8e28c9c1d63
Author: David Mudrák <david@moodle.com>
Date:   Wed, 04 Jan 2017 20:05:03 +0800
Tag:    v2.7.18

MDL-57531 mail: Validate the sender's email address


commit 9267c05fb12db5ee94003c85e0523223e4d546c6
Author: David Mudrák <david@moodle.com>
Date:   Wed, 04 Jan 2017 19:30:18 +0800
Tag:    v2.7.18

MDL-57531 mail: Do not let admins set invalid email addresses


commit 172d31e9a525b38d16806699d6af447c4cbddeb4
Author: David Mudrák <david@moodle.com>
Date:   Wed, 04 Jan 2017 17:58:44 +0800
Tag:    v2.7.18

MDL-56225 mod_forum: Fix inability to edit attachments