* print a warning when var_DelCallback can't find the callback because the
   data doesn't match
 * these warning are only for debug builds.

 * print an error message when the variable creation failed because of a name
   clash (two variables with the same name but different types)
 * print a warning when calling var_Get on a void variable
 * fix one comment as the list is NOT sorted (and that too expensif to do).

Thisway playlist don't run sort when created (in case of you start vlc,
and don't set playlist visible then adding stuff. When you open playlist
it would sort the stuff).

Also remove showing sort-indicator incorrectly on start (don't show
it at all before user clicks to sort).

art url only for the input parent as that's always the same image for all
inputs).

And add two lines that attempt to explain a bit more what is this class about.

Pointed by Olivier Aubert.

Signed-off-by: Michael Hanselmann <public@hansmi.ch>
Signed-off-by: JP Dinger <jpd@videolan.org>

The password can either be directly passed as an option, or it can
be stored in a file whose path is then passed as an option.
Signed-off-by: Michael Hanselmann <public@hansmi.ch>
Signed-off-by: JP Dinger <jpd@videolan.org>

They are an overlook from the removal of the thread serialization