When using absoluteString instead of relativeString I get:
file://localhost/home/fred/GNUstep/Images/TextSystem1.png
There I agree ... IMO the RFCs imply that the hostname part of a file
scheme URL should be an empty string, which would give
file:///home/fred/GNUstep/Images/TextSystem1.png.
However, MacOS-X puts 'localhost' in the hostname position, so the
GNUstep code is written to be compatible with this.
Again this will result in a different MD5 digest than the one expected
by the thumbnail standard, so we wont find the correct file. The
question now is, if there is another method to get the required string
or if this is a bug in GNUstep, which we should correct.
I suggest using the -absoluteString method and removing the 'localhost'
While I think that the MacOS-X implementation is strange, it's the
definitive guide for this class (it's not in OpenStep), so I'de be very
hesitant to 'fix' this and break compatibility.