www/h2o: add CONFLICTS and appease portlint

[dch]

Summary

intentionally not bumping port version

[jrm]

Looks good, but I think this will cause rumblings without a PORTREVISION bump. The policy I am familiar with is: If the package changes, then a PORTREVISION bump is necessary. Maybe if I mention the magic word, @mat, the port genie will appear to set us straight.

[jrm]

I mentioned the policy, but it is probably more important to mention the underlying reason for the policy. I believe that without a PORTREVISION bump, a new package will not be built. With the USE_LDCONFIG= yes change, it seems we would want this, no?

[dch]

If our policy gurus say it should be bumped, then I'm cool with that
but I don't see the need to inflict more unnecessary downloads and
upgrades on the planet than we already do.

FWIW these (from the -devel version) are what's in /usr/local/lib:

/usr/local/lib/libh2o-evloop.so
/usr/local/lib/libh2o-evloop.so.0.15
/usr/local/lib/libh2o-evloop.so.0.15.0-beta1
/usr/local/lib/libh2o.so
/usr/local/lib/libh2o.so.0.15
/usr/local/lib/libh2o.so.0.15.0-beta1

USE_LDCONFIG (at least with my meagre understanding of C & libraries)
is performing no additional function that isn't already in place, as
the port already works. So this USE_LDCONFIG isn't unbreaking anything
and isn't requiring users to update (what would they gain). Let's save
an erg of energy.

[jrm]