This is used by the i386, hp300 and mac68k ports.
- Added exec_aout_prep_oldomagic, and exec_aout_prep_oldnmagic
These are just copies of the respective prep functions from
kern_exec.c with text address starting at 0. Maybe a better fix
is to pass the starting address as a third argument so we don't
duplicate code, but this could be the next pass since the functions
are used in many places. These functions are used for BSDI binaries.
