Reduce the number of placeholders to strict minimum.

apachedex/__init__.py

@@ -112,9 +112,11 @@ def prepareDataForGraph(daily_data, date_format, placeholder_delta,
   append = new_daily_data.append
   for (measure_date_string, apdex, hit) in daily_data:
     measure_date = datetime.strptime(measure_date_string, date_format)
-    while current_date < measure_date:
+    if current_date < measure_date:
       append((current_date.strftime(date_format), 100, 0))
-      current_date += placeholder_delta
+      placeholder_end_date = measure_date - placeholder_delta
+      if placeholder_end_date > current_date:
+        append((placeholder_end_date.strftime(date_format), 100, 0))
     append((measure_date_string, apdex,
       hit * coefficient_callback(measure_date)))
     current_date = measure_date + placeholder_delta