[CREATE] OpenRaster proposal: save currently selected layer

[Andrew Chadwick]

It would be helpful for users if the currently selected layer could be
saved between sessions and restored when loading (see
https://bugs.freedesktop.org/show_bug.cgi?id=37713 ). Let's support a
new attribute on <layer/> to make this possible:

  <stack>
    <layer name="sketch" x="0" y="0" src="data/layer001.png"/>
    <layer name="colours" x="-512" y="-128" src="data/layer002.png"
      selected="selected"/>
  </stack>

A proposal for this up for review at
http://www.freedesktop.org/wiki/Specifications/OpenRaster/Draft/LayerSelectionStatus
. Comments welcome! (Reply-To: set; please use the CREATE list for feedback)

I've chosen W3C-style Boolean attribute notation for XML for this. Hope
that's OK. As far as MyPaint is concerned the selected layer is the same
thing as the layer currently active for editing (though it might be
locked and thus not receive brushstrokes), and there is only one such
layer. Does this proposal need to be extended to support multiple
selection of layers and/or differing concepts of "active", or is what we
have up right now sufficient? If it's insufficient, we could go with an
enumerated type instead.

-- 
Andrew Chadwick