class File
	def File.safe_write(n)
		i = 0
		while File.exists? n + ".#{i}.tmp"
			i += 1
		end
		tmpfd = File.open(n + ".#{i}.tmp", 'w')
		ret = yield tmpfd
		tmpfd.close
		File.rename(n + ".#{i}.tmp", n)
		ret
	end
end