We should first decide what should happen.  While for command line tools
"mv FILE DIR" is established syntax for "mv FILE DIR/`basename FILE`",
I'm not at all sure that shutil.move(src, dst) should do the same.  I
think it should be closer to the UNIX os.rename() semantics which
promises that src *replaces* dst.  If dst is an empty dir, it is removed
using rmdir(); if it is a non-empty dir, the removal fails and hence the
move fails.  I think this is what shutil.move() should do too.  (Even if
it can't make the atomicity promises that UNIX makes.)