[ptx] Bug: cannot load greyscale images

[Michal]

The latest CVS version of hugin doesn't like greyscale images. It prints 
this error while loading image:

06:46:00 PM: Error during image reading:  Precondition violation! 
importImage(): number of bands (color channels) in file and destination 
image differ. (../../src/foreign/vigra/impex.hxx:119)
06:46:00 PM: Error during image reading:  Precondition violation! 
importImage(): number of bands (color channels) in file and destination 
image differ. (../../src/foreign/vigra/impex.hxx:119)
06:46:00 PM: Error during image reading:  Precondition violation! 
importImage(): number of bands (color channels) in file and destination 
image differ. (../../src/foreign/vigra/impex.hxx:119)
06:46:00 PM: Error during image reading:  Precondition violation! 
importImage(): number of bands (color channels) in file and destination 
image differ. (../../src/foreign/vigra/impex.hxx:119)


It was possible to load these images some time ago. But white was 
displayed as red.

Michal