BCO needs string?

[taoeffect]

so that native-packet-dns can log the amount of room that was needed (but not available) to the console.

Meaning, instead of:

BufferCursor.prototype._checkWrite = function(size) {
  if (this._pos + size > this.length)
    throw new BCO();
}

This:

BufferCursor.prototype._checkWrite = function(size) {
  if (this._pos + size > this.length)
    throw new BCO("can't write "+size+' bytes, have room for '+(this.length-this._pos)+' bytes only');
}