Add 'const' to immutable arrays.

lib/formdata.c

@@ -261,7 +261,7 @@ static const char * ContentTypeForFilename (const char *filename,
     const char *extension;
     const char *type;
   };
-  static struct ContentType ctts[]={
+  static const struct ContentType ctts[]={
     {".gif",  "image/gif"},
     {".jpg",  "image/jpeg"},
     {".jpeg", "image/jpeg"},
@@ -1543,7 +1543,7 @@ char *Curl_FormBoundary(void)
                               the same form won't be identical */
   size_t i;
 
-  static char table16[]="abcdef0123456789";
+  static const char table16[]="abcdef0123456789";
 
   retstring = (char *)malloc(BOUNDARY_LENGTH+1);