Code cleanups

on behalf of Lebedev, see issue 1279

rtengine/klt/pnmio.h

@@ -16,20 +16,20 @@
  * used for reading from/writing to files
  */
 unsigned char* pgmReadFile(
-  char *fname,
+  const char *fname,
   unsigned char *img,
   int *ncols, 
   int *nrows);
 void pgmWriteFile(
-  char *fname,
-  unsigned char *img,
+  const char *fname,
+  const unsigned char *img,
   int ncols,
   int nrows);
 void ppmWriteFileRGB(
-  char *fname,
-  unsigned char *redimg,
-  unsigned char *greenimg,
-  unsigned char *blueimg,
+  const char *fname,
+  const unsigned char *redimg,
+  const unsigned char *greenimg,
+  const unsigned char *blueimg,
   int ncols,
   int nrows);
 
@@ -42,14 +42,14 @@ unsigned char* pgmRead(
   int *ncols, int *nrows);
 void pgmWrite(
   FILE *fp,
-  unsigned char *img,
+  const unsigned char *img,
   int ncols,
   int nrows);
 void ppmWrite(
   FILE *fp,
-  unsigned char *redimg,
-  unsigned char *greenimg,
-  unsigned char *blueimg,
+  const unsigned char *redimg,
+  const unsigned char *greenimg,
+  const unsigned char *blueimg,
   int ncols,
   int nrows);