Add SPI transaction code from Ralph Doncaster

- Temporarily comment changes to begin() pending further testing/dev
- Maintain backwards compatibility by detecting Arduino IDE version

RF24.cpp

@@ -367,7 +367,7 @@ void RF24::print_observe_tx(uint8_t value)
 
 void RF24::print_byte_register(const char* name, uint8_t reg, uint8_t qty)
 {
-  //char extra_tab = strlen_P(name) < 8 ? '\t' : '\a';
+  //char extra_tab = strlen_P(name) < 8 ? '\t' : 0;
   //printf_P(PSTR(PRIPSTR"\t%c ="),name,extra_tab);
   #if defined (RF24_LINUX)
     char extra_tab = strlen_P(name) < 8 ? '\t' : 0;
@@ -642,12 +642,16 @@ bool RF24::begin(void)
   //setPALevel( RF24_PA_MAX ) ;
 
   // check for connected module and if this is a p nRF24l01 variant
-  //  
-  setup = read_register(RF_SETUP);
-  if( setup == 0b00001110 )     // register default for nRF24L01P
+  //
+  if( setDataRate( RF24_250KBPS ) )
   {
     p_variant = true ;
   }
+  /*setup = read_register(RF_SETUP);
+  if( setup == 0b00001110 )     // register default for nRF24L01P
+  {
+    p_variant = true ;
+  }*/
   
   // Then set the data rate to the slowest (and most reliable) speed supported by all
   // hardware.

RF24.h

@@ -90,13 +90,17 @@ protected:
    *
    */
   inline void beginTransaction() {
+    #if defined (RF24_SPI_TRANSACTIONS)
     _SPI.beginTransaction(SPISettings(RF_SPI_SPEED, MSBFIRST, SPI_MODE0));
+	#endif
     csn(LOW);
   }
 
   inline void endTransaction() {
     csn(HIGH);
+	#if defined (RF24_SPI_TRANSACTIONS)
     _SPI.endTransaction();
+	#endif
   }
 
 #endif   /* ARDUINO */

RF24_config.h

@@ -53,6 +53,10 @@
 
   #include <Arduino.h>
   
+  #if ARDUINO > 10600
+    #define RF24_SPI_TRANSACTIONS
+  #endif
+  
   // RF modules support 10 Mhz SPI bus speed
   const uint32_t RF_SPI_SPEED = 10000000;