Fixed autoscale check when using null x/y values.

The autoscale check was too broad; it included the case where autoscale
was undefined.  This resulted in axes not expanding correctly when
coordinates at the end of a series had null x or y values.  Fixed by
narrowing the check to !== false; resolves #1095.

jquery.flot.js

@@ -1131,7 +1131,7 @@ Licensed under the MIT license.
                             if (val != null) {
                                 f = format[m];
                                 // extract min/max info
-                                if (f.autoscale) {
+                                if (f.autoscale !== false) {
                                     if (f.x) {
                                         updateAxis(s.xaxis, val, val);
                                     }