Author: Tim Hunt
MDL-42865 Make XMLDB foreign key check more robust.
Otherwise, installing one bad add-on can completely break this report.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=dcc650ef40a78115baa9df1bd1e10fe9fc9bcbb6
http://github.com/moodle/moodle/commit/dcc650ef40a78115baa9df1bd1e10fe9fc9bcbb6
+ 2.5 en [fkunknownfield,tool_xmldb]
+ 2.5 en [fkunknowntable,tool_xmldb]
+ 2.5 en [unknownfield,tool_xmldb]
+ 2.5 en [unknowntable,tool_xmldb]