I made the following changes in 1.6:

• I added a nav beacon to the Sol stargate in Centauri to advertise it. This makes sense since we always place Sol on the galactic map, and since we can assume that people know how to get there.
• I added -void to the normal code for placing stargates. This reduces (but doesn't eliminate) the chance of having a stargate in the middle of nowhere.
• For Centauri and Sirius, I used !void to place stargates. This is already done for binary systems.
• I added the void attribute to labels on sparse asteroid belts (and replaced the asteroid attribute). This makes more sense, since these labels seem to be in the middle of nowhere (because the belts are sparse).