Add or remove the filter in a non-focus list.
These functions add or remove the filter in a non-focus list.
non-focus-list-add-filter if the filter is off, otherwise it calls
non-focus-list-remove-filter (it is used as the callback for the
non-focus-list-add-filter adds a filter is it is not already on, resets the text in it to empty string, and enables it.
non-focus-list-remove-filter removes the filter if it is on.
CAPI User Guide and Reference Manual (Unix version) - 25 Feb 2015