RGB file created by NVIZ2.2

hi, all

i posted that nviz2.2 created a wrong RGB image file. i found that the header
was reverse byte order. so i fixed it at least on FreeBSD.

if you get a broken RGB file, check grass/src/libes/libimage/close.c and
change

-----
#else
  if(image->dorev)
#endif
-----

to

-----
#else
  if(!image->dorev)
#endif
-----

Best Regards,
Huidae Cho