Signed-off-by: Geoffroy Couprie <geal@videolan.org>

- make it case insensitive and sorted alphabetically
- fix a few regressions about config_Get vs. var_Inherit

In skins, slash is the preferred path separator for both Linux and Win32
yet, rather fix those separators and issue a warning than fail to open skins.

This makes drag-and-drop easier, because drag-and-drop pixmap does not
cover the area under mouse cursor.

- Make PlMimeData simply a subclass of QMimeData: destructor of indirect
subclasses of QObject is called even if their direct base class' destructor
is not virtual.
- Protection against using input_item_t* from another VLC instance:
qobject_cast<PlMimeData*>() will fail on QMimeData dropped from another process.
- Some refactoring of PLModel::dropMove() for robustness.

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

A helper object keeps reference count until drag-and-drop is finished.

This enforces the use of qtu() or whatever appropriate.

- Use item ids instead of pointers for drag data to prevent usage after freeing.
- The list of selected items that contitutes drag data is sorted correctly according to item position in tree. This keeps their relative order after drop operation even if they originated from different parent nodes.
- If a parent and any of it's children are selected, only the parent enters drag'n'drop operation. Children are thus not moved out of the parent when dropping.
- Copying by drag and drop performs a recursive copy of all children.

Thanks to Srikanth Raju <srikiraju@gmail.com> for pointing out the problem.

...as the FAQ on http://libsdl.org/ declares this is the most portable
method.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>