pstricks export: why linewidth in centimeters?

[Albert Zihlmann <azihlmann gmx net>]

I don't understand why dia puts the unit "cm" behind its linewidth 
declaration at pstricks export. If I want to scale the image by adding 
the statement "\psset{unit=0.5cm}" before the image file input the image 
shrinks well but all the lines keep their thickness. If I delete 
manually the "cm" from the exported file scaling works fine.

a) Is there a way to turn off this unit output at pstricks export?
b) Or does anyone know an other way to scale such an imported image in a 
latex document?

Thanks, zihlmae