Alter completion for mv

[Daniel <quite@xxxxxxxx>]

I would like completion of the destination argument for mv(1) to first
complete directories. Is this possible by toggling an option, or could
somebody help me out?

The idea is that I most often do this task -- move something to somewhere --
rather than overwriting a file. (In the latter case, perhaps if "-f" is given,
completion should always prefer files).