smb: Report number of bytes used on the filesystem

Calculated the number of bytes used by subtracting the size from the
number of bytes free, as done with local files.

https://bugzilla.gnome.org/show_bug.cgi?id=711838
sftp: Add "PermitLocalCommand no" to the OpenSSH commandline

Add "PermitLocalCommand no" to the OpenSSH commandline to prevent
user-configured commands running and interfering with the sftp session.
This is what the OpenSSH sftp client does.

https://bugzilla.gnome.org/show_bug.cgi?id=639599
fuse: Round up the number of blocks that a filesystem has

If a filesystem is 4095 bytes, indicate that it uses 1 block rather than
0 blocks.

https://bugzilla.gnome.org/show_bug.cgi?id=711855
archive: Set filesystem size information

Set the total size and the amount used to be the total size of the
files; set the amount free to 0.

https://bugzilla.gnome.org/show_bug.cgi?id=711852