[Inkscape-devel] Layer opacity

This got delayed in order to track down and fix the save as ODG crashing bug, but it's in now.

Please give it a good workout to make sure it's solid. It's been pending for a bit, but it gives a lot of benefit to end users. There were no main objects in the Jabber room, and even at least one "the main reason I use layers in gimp". It's gotten a good shakedown with GTK+ 2.6.10, so anyone with 2.8.x would be very welcome to finish running it through it's paces.

(Oh, and for translators, it did bring in one change of adding "Opacity:" to that dialog)