kern/135412: [zfs] [nfs] zfs(v13)+nfs and open(..., O_WRONLY|O_CREAT|O_EXCL, ...)

[Danny Braniss]

hi,
	This pr is realy holding me back, I can't upgrade this server, and
telling serveral tens of users to us cp, etc is not an option. The open
works fine if not using O_EXCL. 

Thanks,
	danny