Fix for overlapping drive icons

Some Puppy users have reported the desktop drive icons getting created on top of each other.

There was a lot of confusion in the Forum discussion, until it became clear that it only happened when the user changed the ROX-Filer "placement granularity" -- the default of which is "fine" (2 pixels).

Once the cause became clearer, K Godt, npierce, MinHundHettePerro and others analysed the problem and proposed solutions, or at least steps to reduce the problem.

npierce has summarised it nicely in a post in this thread, with two possible partial solutions:
http://murga-linux.com/puppy/viewtopic.php?t=86137&start=225

I have implemented #3. Woof commit:
http://bkhome.org/fossil/woof2.cgi/info/faa913cdd5

Tags: woof