The warning message is there in order to tell developers that one of the
rare cases not yet implemeneted were called. This should not cause
the application to stop.
refs #574, #582
Before this change, the model strings were assembled via some
relatives pathes - long and very hard to read. Now it is assembled
via the pattern
<package root dir> <dir> ... <objectname> <texturename>
<package root dir> = the parent directory of xsb_aircrafts.txt
<dir> ... = directory hierarchy down to the object file
refs #574
