Fix seemingly hanging thumbnail preview.

5 secs timeout between slide changes is probably a bit much,
reducing to half a second now. Had the coverflow frequently stuck
at earlier slides otherwise.

Change-Id: Idabe17e1fc8fe2050990a68c357a00dd2d20c08b

android/sdremote/src/org/libreoffice/impressremote/PresentationFragment.java

@@ -263,7 +263,7 @@ public class PresentationFragment extends SherlockFragment {
 
                 if (aSlide == mTopView.getSelectedItemPosition())
                     return;
-                if ((System.currentTimeMillis() - lastUpdateTime) < 5000) {
+                if ((System.currentTimeMillis() - lastUpdateTime) < 500) {
                     return;
                 }
                 mTopView.setSelection(aSlide, true);