Clarify that bounded comparison evaluates x only once
Clarify that bounded comparison evaluates x only once

The old definition

    l<x<u means x>l && x<u

could have been misunderstood to mean that x would be evaluated twice.
Rectify this using 'let'.

gijsleussink/ceylon,gijsleussink/ceylon,gijsleussink/ceylon,gijsleussink/ceylon,gijsleussink/ceylon