This linux-specific completion won't parse /etc/fstab as a lot of people
including myself find it useless. And there is no reliable way to guess
what user wants to mount. Some examples of what is ok for mount:
$ mount /home
$ mount /dev/sda1 /home
$ mount file.iso /media/iso -o loop
$ mount LABEL=mydisk /media/disk
It is more sane to provide just filenames completion for mount.
