I have noticed that mkifs creates a 4 byte trailer to a boot image.  Searches seem to suggest that this is a checksum of
 the image.  We are going to perform system upgrades by writing new images to .altboot and use a custom bootloader to 
copy .altboot to .boot.  We are using the QNX 4 filesystem, which is not power-fail safe.  I have noticed that in some 
cases the image copied into .altboot is the right size but corrupted if the system was hard booted soon after the copy 
is complete.  On bootup, Id like to verify the integrity of .altboot before copying it.  Is the trailer bytes a checksum
 and if so, how do I check it?