Use terminalError when there's a DHCP failure.

I've chosen to flash the error LED twice when there's a DHCP error.
This number is total arbitrary and can definitely be changed; although I
do plan to document these error conditions so we won't want it changing
again and again.

printer.ino

@@ -124,8 +124,7 @@ inline void initNetwork() {
   // start the Ethernet connection:
   if (Ethernet.begin(mac) == 0) {
     debug("DHCP Fail!");
-    // no point in carrying on, so do nothing forevermore:
-    while(true);
+    terminalError(2);
   }
   delay(1000);
   // print your local IP address: