On a Linux system with go-fuse program running as root, the mount is
performed by calling /bin/fusermount, and the unmount is performed with
syscall.Unmount()

This creates a problem on systems (CentOS 6) with a static-but-edited-by-mount
/etc/mtab file.

 - fusermount adds a line to mtab when the go-fuse program starts
 - syscall.Unmount() doesn't edit the file on program exit
 - subsequent invocations of the program fail to mount with:

    "Mount fail: fusermount exited with code 256"

Deleting the now-inaccurate mtab entry clears things up.

There's probably a workaround by adding "-n" option so that mount doesn't
edit mtab in the first place, but it's not obvious where to insert that when
starting with the hello.go example.