Refs: #8830

These parameters will allow to create a slider which adapts to the display.
width/height parameters will be optional. If set, the initial slider will
be resized to meet these requirements.

A main use case will be the possibility to create a fullscreen timeslider
that automatically spans the whole screen whatever the screen resolution.
e.g syntax would be <Slider width="100%" ....>

Till now, these two parameters only had a meaning for geographical positioning.
As explained at http://forum.videolan.org/viewtopic.php?f=26&t=111572,
extending xoffset and yoffset for the general case would help a lot skin
developpers easily position an object of unknown size around a given point :
for instance,
    x="50%" xoffset="-50%" would center an object horizontally.
    x="100%" xoffset="-100%" would set an object to the East

This patch doesn't modify the existing behaviour. It just implements a new
feature for the case where it was a silent no op.

x,y, width, height percentages are computed against the parent container
xoffset and yoffset percentages are computed against the current object

TODO: this approach could be generalized to all objects (need to extend the dtd)

This reverts commit acf5397b.

Conflicts:
	contrib/src/bghudappkit/rules.mak

At the core level, the 'f' hotkey and the double click are managed in a
slightly different way. The former sets up both the playlist and the vout
"fullscreen" variables whereas the latter only sets up the vout variable.

This patch first relies on the vout state if any, and falls back to the
playlist state. This ensures that the fullscreen button always works
consistently for the user. Otherwise, user needs to press twice instead
of once when the playlist and the vout are no longer in sync (after a double
click)

macosx: dialogs provider: fix crash for question dialog and also improve robustness of other dialogs

as reported on the forum at http://forum.videolan.org/viewtopic.php?f=26&t=111572

plus factorise some code.

This fixes a bug reported on the forum at
http://forum.videolan.org/viewtopic.php?f=26&t=111572

Close: #8830

If a pre-2.1 version is detected it will be uninstalled silently before
proceeding.