database MDL-24863

- added restricting text conditions to where_clause , it throws a dml_exception when detected.
- also added to where_clause throwing dml_exception for field that doesn't exist in table.
- added unit tests for text condition restricting.
- added 2 unit tests for set_field_select() testing 'auto-casting params to int problem' fix

lang/en/error.php

@@ -442,6 +442,7 @@ $string['storedfileproblem'] = 'Unknown exception related to local files ({$a})'
 $string['tagdisabled'] = 'Tags are disabled!';
 $string['tagnotfound'] = 'The specified tag was not found in the database';
 $string['targetdatabasenotempty'] = 'The target database is not empty. Transfer aborted for safety reasons.';
+$string['textconditionsnotallowed'] = 'Comparisons of text column conditions are not allowed. Please use sql_compare_text() in your query.';
 $string['themenotinstall'] = 'This theme is not installed!';
 $string['TODO'] = 'TODO';
 $string['tokengenerationfailed'] = 'Cannot generate a new token.';