ext3: Add replace-on-rename hueristics for data=writeback mode
In data=writeback mode, start an asynchronous flush when renaming a
file on top of an already-existing file. This lowers the probability
of data loss in the case of applications that attempt to replace a
file via using rename().
If you aren't sure, I recommend using ext3 with the explicit data=ordered option until you've had the opportunity to sit down and understand the data=writeback and/or ext4 semantics.