127.0.0.1 vs localhost and dogstatsd

[apiology]

Hi!

The docs here don't talk about which dogstatsd hostname clients should point to (127.0.0.1), and I think the docs should.

It may seem intuitive to those familiar with buildpacks that the agent runs on the same dyno as the user's deployed code, but even then there's a hangup - it appears that the datadog agent will not accept messages sent to 'localhost', whereas '127.0.0.1' works fine. I assume that's because 'localhost' traffic ends up coming in via something other than the local network interface, and the agent won't accept non-"local" traffic unless the DD_DOGSTATSD_NON_LOCAL_TRAFFIC env variable is set.