Listbox,SelectionTool: use make_query instead of crafting URL manually

Using make_query makes sure that the query parameters are properly
encoded and also change selection_index to become an int, because
it keeps the type of parameters.

As a consequence, we had to adjust a few place in the code where
selection_index was tested for truthiness: because "0" as a string is
true, but 0 as an int is not. For that, we changed to test the presence
of selection_name instead of testing selection_index, as they are always
used together.

This fixes a problem that & in URL was encoded twice for listbox
anchor links ( bug_module/1137 )