shares-admin does not handle spaces in paths correctly

[Daniel U. Thibault]

If you use shares-admin to share a folder via NFS (Shared Folders: Shared Folders: Add) and you pick out a path that includes embedded spaces, the string is included verbatim (that is, without escaping the spaces) in the configuration (/etc/exports in particular), and thus the share will utterly fail.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: gnome-system-tools 3.0.0-3ubuntu4.1
ProcVersionSignature: Ubuntu 3.13.0-53.89-generic 3.13.11-ckt19
Uname: Linux 3.13.0-53-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Mar 3 13:24:20 2016
ExecutablePath: /usr/bin/shares-admin
InstallationDate: Installed on 2014-12-17 (442 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
SourcePackage: gnome-system-tools
UpgradeStatus: No upgrade log present (probably fresh install)