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.