Fixing the prototype for my_strndup() to compile on Windows.

mysys/my_malloc.c:
  Changing prototype for my_strndup().
server-tools/instance-manager/parse.h:
  Changing prototype for my_strndup().

mysys/my_malloc.c

@@ -83,7 +83,7 @@ char *my_strdup(const char *from, myf my_flags)
 }
 
 
-char *my_strndup(const byte *from, uint length, myf my_flags)
+char *my_strndup(const char *from, uint length, myf my_flags)
 {
   gptr ptr;
   if ((ptr=my_malloc(length+1,my_flags)) != 0)

server-tools/instance-manager/parse.h

@@ -69,7 +69,7 @@ private:
 
 inline char *Named_value::alloc_str(const LEX_STRING *str)
 {
-  return my_strndup((const byte *) str->str, str->length, MYF(0));
+  return my_strndup(str->str, str->length, MYF(0));
 }
 
 inline char *Named_value::alloc_str(const char *str)