Git commits in Moodle 3.6.4 by David Mudrák

commit 7fb7ab13dc1d11affdeb1717d1406c62c61e9508
Author: David Mudrák <david@moodle.com>
Date:   Fri, 10 May 2019 16:32:42 +0800
Tag:    v3.6.4

MDL-65537 lang: Use fixed strings in tests, too

commit a825339917ec5c4e058de9e863182f0cb7e02f66
Author: David Mudrák <david@moodle.com>
Date:   Thu, 14 Mar 2019 04:28:48 +0800
Tag:    v3.6.4

MDL-64994 analytics: Improve the Python package version check

commit 6b1ce978946dc1c978ae7db646fad0d394aa8507
Author: David Mudrák <david@moodle.com>
Date:   Wed, 06 Mar 2019 03:01:28 +0800
Tag:    v3.6.4

MDL-64996 analytics: Make sure the no_teaching model is trained

commit 38ce5978dd14695da8f02a55c957487340a5a807
Author: David Mudrák <david@moodle.com>
Date:   Wed, 06 Mar 2019 02:57:52 +0800
Tag:    v3.6.4

MDL-64996 analytics: Don't mark static model as untrained after clearing

commit 0e91160efe5590c2b7456ab80a55b9cc7b5d186a
Author: David Mudrák <david@moodle.com>
Date:   Tue, 05 Mar 2019 20:47:14 +0800
Tag:    v3.6.4

MDL-64994 analytics: Add a simple semantic version check method