This is implimented by defining macro's that take the mode into account when get/set/checking the selection and that a face can be drawn.
When this is enabled, things work a bit differently
* all faces are drawn in the UV view (except hidden faces).
* selecting faces/verts in the UV window selects them on the mesh also and vice vercer.
* when EditMode (Face only) is enabled, selecting faces in the UV view is not sticky.
* hiding/(de)select all and invert selection simle call the editmesh functions.
* there is no way to select 1 uv corner of 1 face (because a mesh cannot have this as a valid selection) either all UV's that use a vert (sticky), or the whole face.
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