rewrite 0U - VSL_SEGMENTS in way which should make Flexelint happy
rewrite 0U - VSL_SEGMENTS in way which should make Flexelint happy

We intentionally provoke an early wrap of our segment_n unsigned int.
The previous code is fine according to
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
"A computation involving unsigned operands can never overflow...",
but nevertheless we don't want to trigger Flexelint warnings.

Thanks to Dag Haavi Finstad for digging the ISO standards url.

mrhmouse/Varnish-Cache,franciscovg/Varnish-Cache,zhoualbeart/Varnish-Cache,varnish/Varnish-Cache,mrhmouse/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,zhoualbeart/Varnish-Cache,mrhmouse/Varnish-Cache,mrhmouse/Varnish-Cache,varnish/Varnish-Cache,zhoualbeart/Varnish-Cache,zhoualbeart/Varnish-Cache,feld/Varnish-Cache,franciscovg/Varnish-Cache,franciscovg/Varnish-Cache,varnish/Varnish-Cache,chrismoulton/Varnish-Cache,ajasty-cavium/Varnish-Cache,chrismoulton/Varnish-Cache,gquintard/Varnish-Cache,franciscovg/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,varnish/Varnish-Cache,ajasty-cavium/Varnish-Cache,chrismoulton/Varnish-Cache,ajasty-cavium/Varnish-Cache,gquintard/Varnish-Cache,chrismoulton/Varnish-Cache,zhoualbeart/Varnish-Cache,ajasty-cavium/Varnish-Cache,gquintard/Varnish-Cache,varnish/Varnish-Cache,ajasty-cavium/Varnish-Cache,chrismoulton/Varnish-Cache,franciscovg/Varnish-Cache,mrhmouse/Varnish-Cache