Memory leak when closing a figure window

[ThomasLeMezo]

The memory is not cleaned when closing a window. Test case: draw 1000 lines with more than 10000 points per lines (i.e. to get more than 400MB for a figure). Memory doesn't come back to its initial value when closing the figure window.
The effect is a saturation of memory after drawing several figures which makes necessary to close VIBES and re-open it.

The bug seems to only appears when drawing lines and not pave (to be confirm)