snapshot rename does not unmount it

[Richard Kojedzinszky]

Dear zfs-devel list,

Gerrit Kühn <gerrit.kuehn at aei.mpg.de> reported that renaming a snapshot, 
and after listing them in .zfs/snapshot/ dir shows some error. Attached a 
script which will demonstrate it. I found that (with git bisect) that 
https://github.com/freebsd/freebsd/commit/7c87858955593be19a80e57b7353b09f5587ae9b 
is causing the wrong behaviour, but unfortunately that commit is too big 
for me to understand.

Thanks in advance,

Kojedzinszky Richard