astyle iexamine::egg_sackbw and iexamine::egg_sackws
Combine the code of iexamine::egg_sackbw and iexamine::egg_sackws into one function.

Use closest_points_first to get possible spots for spiderlings.
Better name for counter variable.
Use game::is_empty to check for place to spawn spiderlings, prevent monsters from spawning in walls.
Prevent egg sacks from being created in solid terrain.