Fixed default manual sort order in icon view.

Caja didn't correctly use 'manual sort order' option in icon view.
Now after setting:
$ gsettings set org.mate.caja.preferences default-sort-order manually
we have the default manual layout.

This was changed in e13142565949e577ae589c0e93527b6698614281 probably accidentaly.
I have reverted to the similar code as it was in 1.2 branch but now
with using gsettings.

Similar patch should be made for 1.8 branch.