MDL-35958 mod_data: backport of MDL-34448 members of seperate groups can see database entries for other groups.
MDL-38225 - data: Database entries are now linked correctly.

This was a regression that was fixed in the 2.x versions but not 1.9
Merge branch 'mdl19_MDL-35958' of git://github.com/danmarsden/moodle into MOODLE_19_STABLE
on-demand release 1.9.19+