mount: decode paths from mountinfo (v2)

mountinfo contains mangled paths. space, tab and back slash were
replaced with usual octal escape, so we need to replace these charecter
back.

v2: declare cure_path as static
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>