if the applet is not found, return the exit status 127 instead of 1 as the POSIX standard suggests:
http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_08_02

This is useful for scripting purposes, for instance:
echo 1+2 | busybox bc
if [ $? -ne 127 ]; then ...