Another function pair required for serialisation; these ones save

Another function pair required for serialisation; these ones save
and restore anything vitally important in the game_ui. Most of the
game_ui is expected to be stuff about cursor positions and currently
active mouse drags, so it absolutely _doesn't_ want to be preserved
over a serialisation; but one or two things would be disorienting or
outright wrong to reset, such as the Net origin position and the
Mines death counter.

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@6026 cda61777-01e9-0310-a592-d414129be87e