chg: defer shutdown in slClose()
(cherry picked from commit 96d98ec5e074988d6acae83de7646fc65aa7382b)

Signed-off-by: Andreas Steenpass <steenpass@mathematik.uni-kl.de>

Conflicts:
	Singular/silink.cc
Merge pull request #433 from steenpass/slClose_sw

chg: defer shutdown in slClose()
chg: singularsurf/surf/display instead of gtk-surf