This code supports MaxMind's GeoIP geotargeting database.

I took the original geoip.inc library provided by maxmind and added
shared memory support to it.

I will likely strip it down to a lightweight shared-memory-only version
to improve its performance when integrated into the delivery code.

On a 533 MHz Athlon system, a lookup took 0.003 seconds.  On a dual-processor
2GHz PIV Xeon, it took 0.0009 seconds.

My benchmarks of 160 requests per second were on a dual 933 MHz system.
I would estimate that on such a system, the lookup time would be about
0.002 s, which would drop performance to about 120 requests per second.
Of course, this doesn't really account for the extra time required
to load the geoip code into the delivery process...
