[ptx] New hugin tutorial - Stitching flat scanned images

[Bruno Postle]

I've added another hugin tutorial, since this is a subject that 
comes up again and again:

  http://hugin.sourceforge.net/tutorials/scans/

Please comment.  In particular I'm sure that there was previously a 
way to optimise lens parameters for each image individually without 
automatically optimising them for every lens.  This tutorial says to 
edit the script before optimising, which is less than ideal.

(Note that my rate of producing tutorials is a bit less than one a 
year, so more contributions are very welcome)

-- 
Bruno