begin() returns false when chip not detected, fixes #53

SerialFlashChip.cpp

 	pinMode(pin, OUTPUT);
 	CSRELEASE();
 	readID(id);
+	if ((id[0]==0 && id[1]==0 && id[2]==0) || (id[0]==255 && id[1]==255 && id[2]==255)) {
+		return false;
+	}
 	f = 0;
 	size = capacity(id);
 	if (size > 16777216) {

examples/CopyFromSerial/CopyFromSerial.ino

   //SPI.setMOSI(MOSI);  // uncomment these if using the alternate pins
   //SPI.setMISO(MISO);
   //SPI.setSCK(SCK);
-  SerialFlash.begin(CSPIN);
+  if (!SerialFlash.begin(CSPIN)) {
+    while (1) {
+      Serial.println("Unable to access SPI Flash chip");
+      delay(1000);
+    }
+  }
+
 
   //We start by formatting the flash...
   uint8_t id[5];

examples/EraseEverything/EraseEverything.ino

   while (!Serial && (millis() - startMillis < 10000)) ;
   delay(100);
 
-  SerialFlash.begin(FlashChipSelect);
+  if (!SerialFlash.begin(FlashChipSelect)) {
+    while (1) {
+      Serial.println("Unable to access SPI Flash chip");
+      delay(1000);
+    }
+  }
   unsigned char id[5];
   SerialFlash.readID(id);
   unsigned long size = SerialFlash.capacity(id);

examples/RawHardwareTest/RawHardwareTest.ino

   delay(100);
 
   Serial.println("Raw SerialFlash Hardware Test");
-  SerialFlash.begin(FlashChipSelect);
+  SerialFlash.begin(FlashChipSelect); // proceed even if begin() fails
 
   if (test()) {
     Serial.println();