Fix in-memory filesystem reserved space

[cddesire]

public boolean reserveSpace(Path f, long size) {
      synchronized (this) {
        if (!canFitInMemory(size))
          return false;
        FileAttributes fileAttr;
        try {
          fileAttr = new FileAttributes((int)size);
        } catch (OutOfMemoryError o) {
          return false;
        }
        totalUsed += size;
        tempFileAttribs.put(getPath(f), fileAttr);
        return true;
      }
    }

[cddesire]

done