[Unionfs] Volume full -> Filesystem full

[Simon Sasburg]

> A long while back there were patches floating around to make unionfs merge
> space as well, but those were for the (now ancient) 1.x code base.

I've actually been working a bit on some new patches to do this
(spreading new files to be created on the branch with the most free
space), and they were working quite well for some time too.

Recently i had some stability problems though, so i went back to plain unionfs.
This didn't solve the problems though, so it may not have been my
patches that caused them.

Another problem with my patches was that they were a bit hacky in that
they just disabled the whiteout/opaque dir markers, cause they caused
some problems with the spreading of newly created files. (and for my
use case i didn't need them anyway :-p)

I doubt my patches in their current state are useful to anyone but me. :-)
I will probably look into this again sometime, but i can't say for
sure when that will be. It might be a good idea to see how to make
this new behaviour configurable so it plays nice without breaking the
rest of unionfs, but i hadn't gotten that far yet...

Simon Sasburg