Comment 13 for bug 1090685

I changed it now so that the unhide/purge buttons are only enabled if there are some tracks selected. The "select all" button is a bit more complicated as it should also change depending on the search results. So right now it is enabled all the time like in dlgprepare.* for consistency.

To also disable it depending on how many songs are shown I will have to find a way to get the number of displayed tracks after a search.

could you please look over this patch aswell. I only changed dlghidden.h/cpp dlgmissing.h/cpp