numbers passed in instead of using a BEGIN construct. nawk didn't like
the hex escapes used there.
Fixes a problem reported by Shin'ichiro TAYA on port-powerpc.
Use "int(NUMBER)%256" instead of just "NUMBER" in the printf "%c"
statements in the awk script. nawk was appearing to refuse outputing
a 0 byte of the low eight bits of the number were 0 but any higher
bits were set.
walnut-mkimg.sh tested using gawk, nawk and mawk.
cd019fdfb8