[Inkscape-devel] new keys in node editor

Please test!

New keys in node editor: * esc deselects and cancels rubberband and node dragging * ctrl-a selects all nodes * tab and shift-tab cycle through nodes of the current shape

All these keys work across all subpaths of a shape. Note that I had to change the lists of nodes, subpaths, and selected nodes from single-linked to double-linked.