long hangs when deleting large directories (3.0-rc3)

[Michael Weissenbacher]

Hi Marcus / Dave!
> 
> This completely fixes the issue. As a bonus "rm -fr && sync" completes
> much quicker now.
> ...
> So many thanks Dave. Your prompt help is very much appreciated.
> 
I just wanna add that i've seen these kinds of hangs too when removing
directories with millions of files. My "solution" was to recreate the
filesystem - which was several years old at that time. Looking forward
to the fix. Thanks for the great work going on here - both for the
in-depth investigation and the fix.

cheers,
Michael