fix possable race condition in Cursor

It is possable to seen a late modification timestamp change after file size has changed. 
// host-time  file-size  file-modified-time
//    12:00      50k          12:00
//    12:01      51k          12:00
//    12:02      51k          12:01 <- 
If this happens, and nothing new is written after sleepped 1s in line 293, Cursor will resetRAF and read this file from beginning again !