Fix compiler warnings

SD.cpp

 #define MAX_COMPONENT_LEN 12 // What is max length?
 #define PATH_COMPONENT_BUFFER_LEN MAX_COMPONENT_LEN+1
 
-bool getNextPathComponent(char *path, unsigned int *p_offset,
+bool getNextPathComponent(const char *path, unsigned int *p_offset,
 			  char *buffer) {
   /*
 
 
 
 
-boolean walkPath(char *filepath, SdFile& parentDir,
+boolean walkPath(const char *filepath, SdFile& parentDir,
 		 boolean (*callback)(SdFile& parentDir,
 				     char *filePathComponent,
 				     boolean isLastComponent,
 //}
 
 
-boolean SDClass::exists(char *filepath) {
+boolean SDClass::exists(const char *filepath) {
   /*
 
      Returns true if the supplied file path exists.
 //}
 
 
-boolean SDClass::mkdir(char *filepath) {
+boolean SDClass::mkdir(const char *filepath) {
   /*
   
     Makes a single directory or a heirarchy of directories.
   return walkPath(filepath, root, callback_makeDirPath);
 }
 
-boolean SDClass::rmdir(char *filepath) {
+boolean SDClass::rmdir(const char *filepath) {
   /*
   
     Makes a single directory or a heirarchy of directories.
   return walkPath(filepath, root, callback_rmdir);
 }
 
-boolean SDClass::remove(char *filepath) {
+boolean SDClass::remove(const char *filepath) {
   return walkPath(filepath, root, callback_remove);
 }
 

SD.h

   File open(const char *filename, uint8_t mode = FILE_READ);
 
   // Methods to determine if the requested file path exists.
-  boolean exists(char *filepath);
+  boolean exists(const char *filepath);
 
   // Create the requested directory heirarchy--if intermediate directories
   // do not exist they will be created.
-  boolean mkdir(char *filepath);
+  boolean mkdir(const char *filepath);
   
   // Delete the file.
-  boolean remove(char *filepath);
+  boolean remove(const char *filepath);
   
-  boolean rmdir(char *filepath);
+  boolean rmdir(const char *filepath);
 
 private:
 

utility/Sd2Card.cpp

   while (!(SPI0_SR & SPI_SR_TCF)) {}
 }
 /** SPI send multiple bytes */
+#if 0
 static void spiSend(const uint8_t* output, size_t len) {
   // clear any data in RX FIFO
   SPI0_MCR = SPI_MCR_MSTR | SPI_MCR_CLR_RXF | SPI_MCR_PCSIS(0x1F);
     nf--;
   }
 }
-
+#endif
 
 
 
  */
 uint8_t Sd2Card::readData(uint32_t block,
         uint16_t offset, uint16_t count, uint8_t* dst) {
-  uint16_t n;
+  //uint16_t n;
   if (count == 0) return true;
   if ((count + offset) > 512) {
     goto fail;

utility/SdFile.cpp

       if (!f.remove()) return false;
     }
     // position to next entry if required
-    if (curPosition_ != (32*(index + 1))) {
+    if (curPosition_ != (uint32_t)(32*(index + 1))) {
       if (!seekSet(32*(index + 1))) return false;
     }
   }