Make chainsaw drops item on ground properly + handle drop with numbers
and not some hackish try 8 times before giving up and dropping at original pos
fix https://github.com/minetest-technic/technic/issues/137 and https://github.com/minetest-technic/technic/issues/147
Chainsaw drops are forced to drop on the ground, whether the location of
the drop is below ground or floating above ground

This also cleans up the code style of chainsaw.lua.