9737ffe092
The masking filter now has a default fill value, so that if a provided value does not match, then "X" is used. The tests were modified to use "Y" as an explicitly provided fill value (to distinguish from the default "X") and the results were the default fill value would kick in were modified accordingly.
Note that if modifications are made to any of the t/*-files and the r/*-files are regenerated, the output MUST BE CHECKED MANUALLY to ensure that the produced result indeed is the expected. Otherwise the mysqltest-based tests effectively tests nothing.