Adding two new functions: sql_isempty() and sql_isnotempty() to perform SQL comparisons to empties in a cross-db way. General solution for problems like MDL-12084
Adding two new functions: sql_isempty() and sql_isnotempty() to perform
SQL comparisons to empties in a cross-db way. General solution for
problems like MDL-12084

Merged from MOODLE_19_STABLE

dilawar/moodle