Reject invalid audio drivers

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4906 c046a42c-6fe2-441c-8c8c-71466251a162

configure

@@ -795,6 +795,16 @@ for drv in $audio_drv_list; do
         "pa_simple *s = NULL; pa_simple_free(s); return 0;"
     ;;
 
+    *)
+    echo "$audio_possible_drivers" | grep -q "$drv" || {
+        echo
+        echo "Error: Unknown driver '$drv' selected"
+        echo "Possible drivers are: $audio_possible_drivers"
+        echo
+        exit 1
+    }
+    ;;
+
     esac
 done