The GeoIP resolver keeps a permanent open file descriptor on the
GeoIP database file, for example /usr/share/GeoIP/GeoIPCity.dat
Because we initialize a resolver for each registry, servers with
many databases may easily blow up the open file descriptor limit
of multi-threaded workers (gevent or no workers multithread mode).
The Maxmind GeoIP API appears to be thread-safe since v1.1.4, so
it is much less wasteful to use a shared resolver for each process.
This patch keeps the _geoip_resolver class attribute on `ir.http`
for compatibility, but it will be removed for the next version.
Olivier Dony
76c36079a5