[Support #EYX-317866]: gribtonc for WRF post-processed files

Themis,
the levels 206, 207, 248,249, 251, and 252 were missing in the code, so I added them. I didn't have a file to test them so hopefully it's correct. There is a new decoders release decoders-4.1.2.tar.Z or get decoders.tar.Z Let me know how it works out.The new code is on the decoders ftp. 
robb...