Snapshot the backend polling code without the advanced math.

Snapshot the backend polling code without the advanced math.

Presently we only record th state of the last 64 tries to poll the
backend in a shift register, which can be show with the interrim
CLI command "debug.health":

Health stats for backend b0
Oldest __________________________________________________ Newest
4444444444444444444444444444444444444444444444444444444444444444 Good IPv4
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Good Xmit
SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS Good Shut
RR-RR-R-RRRR---RR-RR-R-R-R-R-R-RRRR-RR-----RR--RRRR--RRR-R-----R Good Recv

More to follow.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@3084 d4fa192b-c00b-0410-8231-f00ffab90ce4