Update GTK icon theme after installing KDE

Otherwise GTK will be confused about older cache and icons won't work in
GTK-based widgets.

Related to QubesOS/qubes-issues#2968

kde-settings-qubes.spec.in

@@ -12,6 +12,7 @@ BuildRequires: make
 
 Requires: qubes-desktop-linux-common
 Requires: qubes-artwork
+Requires: kde-gtk-config
 Requires: kde-filesystem
 Requires: kde-runtime
 Requires: kde-runtime-flags
@@ -125,5 +126,22 @@ if [ -r "$backupfile" ]; then
     mv -f "$backupfile" "$configfile"
 fi
 
+touch --no-create %{_kde4_iconsdir}/hicolor ||:
+touch --no-create %{_kde4_iconsdir}/breeze ||:
+
+%posttrans
+gtk-update-icon-cache --quiet %{_kde4_iconsdir}/hicolor ||:
+gtk-update-icon-cache --quiet %{_kde4_iconsdir}/breeze ||:
+update-desktop-database -q ||:
+
+%postun
+if [ $1 -eq 0 ] ; then
+  touch --no-create %{_kde4_iconsdir}/hicolor ||:
+  touch --no-create %{_kde4_iconsdir}/breeze ||:
+  gtk-update-icon-cache --quiet %{_kde4_iconsdir}/hicolor ||:
+  gtk-update-icon-cache --quiet %{_kde4_iconsdir}/breeze ||:
+  update-desktop-database -q ||:
+fi
+
 %changelog
 @CHANGELOG@