Ignore first sample from ADC

ADC of AVR contains a 'bug' that causes first sample to be corrupt. Fixed in
code now.

wordclock/wordclock.ino

@@ -194,6 +194,9 @@ void setup()
   pinMode(LED4PIN, OUTPUT);
 
   analogReference(DEFAULT);
+  // known 'bug' in AVR ADC: after switching analog reference, first sample
+  // could be corrupt and should be ignored --> discard this sample now
+  analogRead(LIGHTSENSOR_INPUTPIN);
 
   current_brightnes=MAXBRIGHTNESS;