DetectOS - Tries to detect which OS the script is run under

Usage: detectos

This script tries to detect if it's running under AmigaOS3 (or older), 
AmigaOS4, MorphOS or AROS. It does this by checking the version or existance
of various libraries. For now it only reports back:
os3 - under any old version of AmigaOS
os4 - when run under AmigaOS 4
mos - when run under MorphOS
aros-i386 - when run under AROS, currently does not detect architecture or
            ABI version.