When Krusader users utilize some comboBoxes on the search dialog: they often
see bad suggestions because there are obsolete entries, mistakes and so on, but
normal Krusader users can't remove those entries. For example, web browsers have
Shift+Del in order to remove the thwarting entries.

If the KrHistoryComboBox class is used, then Krusader users are able to
delete wrong entries from history lists, and therefore they can remove those bad
suggestions that they were seeing.

Press Ctrl+S to see the search dialog. Using the "Contains text"
comboBox on the Search dialog, several times: add a new search term, search with
it, delete the search term:
a) using Shift+Del when the popup list is seen;
b) or using the arrow keys and Shift+Del when the popup list is not visible;
monitor the changes in the ~/.config/krusaderrc file. Try to delete all
the search terms until the list is empty, press Shift+Del again.

Press

Ctrl and +

and perform equivalent tests.

Press

Ctrl and -

and perform equivalent tests.

Press Ctrl+S to see the search dialog. Using the "Exclude Folder Names"
comboBox on the Search dialog, several times: add a new {folder name to be
excluded}, search using it, delete the {folder name to be excluded}:
a) using Shift+Del when the popup list is seen;
b) or using the arrow keys and Shift+Del when the popup list is not visible;
monitor the changes in the ~/.config/krusaderrc file. Try to delete all
the {folder names to be excluded} until the list is empty, press Shift+Del
again.

Search text inside the files of a folder, just in case.

Note: Those changes are designed to be tried after applying the ones
described in https://phabricator.kde.org/D28959