Add gamma support to ply-image.

src/ply-image.c

Index: src/ply-image.c
diff --git a/src/ply-image.c b/src/ply-image.c
index 3395c9200b6d3697678562d79b786d510cf27e8f..168ecb8491b9372f79864f063631426a59aa7d67 100644
--- a/src/ply-image.c
+++ b/src/ply-image.c
@@ -451,6 +451,7 @@ ply_image_from_file(const char *path)
 }
 
 #include "ply-frame-buffer.h"
+#include "ply-gamma.h"
 
 #include <math.h>
 #include <signal.h>
@@ -562,6 +563,8 @@ main (int    argc,
       return exit_code;
     }
 
+  ply_gamma_set();
+
   if (clear)
     {
       ply_frame_buffer_clear (buffer);