java architecture names and s390x

[peter green <peter.green@postgrad.manchester.ac.uk>]

Thanks niels for the speedy fix to armhf/sh4/powerpcspe issues in 
java-arch.sh.

Unfortunately i've just spotted another issue on s390x the location of 
libjvm.so seems to be

/usr/lib/jvm/java-6-openjdk-s390x/jre/lib/s390x/server

However java-arch.sh appears to (from looking at the code and looking at 
build
logs, I don't have access to a s390x machine myself) return "s390" on 
s390x systems.