fix mass and off-by-one errors

vacation.p8

@@ -417,8 +417,8 @@ mknew(fuzzy, function(x)
  local p = (x.p or fuzzy.p) & 0xffff
  x.mass = 0
  while p ~= 0 do
-  x.mass += p & 0x8000
-  p = p << 1
+  x.mass += p & 1
+  p = (p >>> 1) & 0xffff
  end
 end)
 
@@ -427,7 +427,7 @@ function fuzzy:update()
  if (self.n < self.interval) return
  self.n = 0
  for i=1,self.tries do
-  local b = 1 << rnd(15)
+  local b = 1 << rnd(16)
   if b & self.p == 0 then
    if i == self.tries or not self.weight or self.mass <= self.weight then
     self.mass += 1