This also fixes error handling: if the thread cannot be created, we do
fail cleanly.

This allows using it at another time than destroying the object

...and less prone to deadlocks. This restarts until all keys are NULL,
in case cleaning up reset one key back to a non-NULL value.
There is still a slight difference with POSIX still. POSIX will restarts
only after all destructors have been invoked, not after the first one.

In practice, this bug was hidden by another bug in the thread variables
implementation: the destruction callback is never invoked.

This reverts commit eea468e6.

When the media is played, the formats represent decoder output, and the ids are not preserved (video ES can be replaced by audio ES)

This reverts commit 708a15ff.

Default skin becomes slightly transparent when moved.
(deactivated by default, needs to be set up in preferences)

Several redraw were no longer needed
(tested successfully on Ubuntu/metacity and WinNT)

On Win32, switching back and forth between layered Window and not layered
 window (case where only one of the two alpha parameters is < 255) was removed
because display was not satisfactory. (transition a bit weird)

This tiny patch enables opening of VideoCD/AudioCD/DVD discs with VLC in KDE when inserted, which was broken before.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

The default skins now benefits from relative positioning:
   - main window centered
   - playlist window centered with a 5% offset
   - fullscreen controller centered at the bottom
     of the screen with a 3% margin from the border
   - other ancillary windows all centered

So far in skins2, all x, y, width and height were given in pixels, and
no reference to the screen resolution could be made.

This patch implements the following :
- all x, y, width, height can be given in pixels or in % of their container.
  For windows, the container is the screen. For widgets, it can be the
  layout or a panel.
- Five new tags eases up positioning
  - position : relative position given as "Center", "West", "NorthWest", ...
  - x/y-margin : margins to take into account (in px or %) wrt the borders.
  - x/y-offset : additional offset to apply (in px or %).
- the image control can now accept a width and a height parameters.

On most WM, move and resize are noop as long as the window is not visible, and
these calls have to be reissued once the window becomes visible.
  - so avoid unnecessary calls when there are known to be noop.
  - remove a move in TopWindow that appears hackish
    (it hides a MoveResize and is actually needed for _all_ windows)

A good practice is to invalidate the window and leave it to the OS to decide if a repaint is or not needed.

As a side effect, this fixes some alternative task switchers (alt-tab) on WinNT (like TaskSwitcher or ATTv) that displayed a black rectangle instead of the preview of the skin, because the skin engine was not doing things the usual way.

Events like WM_PAINT should be processed in the WinProc, because
some functions directly call the WinProc (e.g UpdateWindow())

Don't do anything if the image doesn't change. Otherwise, some unpleasant
flickering occurs when the image is animated.

All UI related operations in Qt4 must be done on the UI thread, as
QtGui is not thread-safe internally.

LibVLC applications can now select their video memory format when the
video output is created. In particular, this allows preservation of the
original pixel dimensions.

While untested, this should also enable planar YCbCr rendering. Until
this, vmem assumed that all planes had equal pitches, so that subsampled
planes would not really work.