setup-helper: add alsa-lib to inject_packages

as of version 3.5 xulrunner depends on alsa-lib. If someone updates
the system with firefox 3.0.x installed we have to inject the lib.

iso/bin/setup-helper

@@ -99,6 +99,10 @@ if [ `is_installed xorg` ]; then
     inject_packages xorg-dri2proto
 fi
 
+if [ `is_installed xulrunner` ]; then
+    inject_packages alsa-lib
+fi
+
 # module-init-tools, ticket #437
 if [ -f $ROOT/etc/modprobe.conf ]; then
     mkdir -p $ROOT/etc/modprobe.d/