gddo-server: add a trust proxy flag identify requests by real ip.

X-Real-Ip is used as the remote address to identify the original
address sent through the requests to detect robots.

This fixes golang/gddo#393

Change-Id: I322061dd355340d864376e656185bd84fbbc9432
Reviewed-on: https://go-review.googlesource.com/21996
Reviewed-by: Andrew Gerrand <adg@golang.org>
1 file changed