Git commits in Moodle 3.5.6 by Paul Holden

commit 29fcc59f88fee5144eb8a56b4c04c38050ee9544
Author: Paul Holden <pholden@greenhead.ac.uk>
Date:   Wed, 27 Mar 2019 20:01:42 +0800
Tag:    v3.5.6

MDL-65197 editor: handle empty user preference in privacy export.

commit 546ea1217996785cd474ffbf7e1cad02d98f7165
Author: Paul Holden <pholden@greenhead.ac.uk>
Date:   Fri, 08 Mar 2019 22:40:41 +0800
Tag:    v3.5.6

MDL-46931 roles: retrieve distinct users in sub-query.

commit 4418ec941168811fe6cc5fa4758ae399a669d7e0
Author: Paul Holden <pholden@greenhead.ac.uk>
Date:   Fri, 08 Mar 2019 20:32:24 +0800
Tag:    v3.5.6

MDL-43130 access: fix user counting when retrieving assignable roles.