Keep Alive Problem reported and patched by Christian Schneider
 Also reported by Hiroyuki OYAMA and Vladimir Klebanov
mod_rpaf was incorrectly using r->pool to allocate memory for the
ip. The correct pool for this when you are dealing wth keep-alive
requests was r->connection->pool.

Adding configurable header to work with common Russian setups that
use X-Real-Ip instead of X-Forwarded-For.

Fixing problems with keep-alive connections reusing the original
X-Forwarded-For ip as the 'remote_ip'. 

Move the `change_remote_ip' handler from being APR_HOOK_MIDDLE to
APR_HOOK_FIRST to make the module run before modules like mod_geoip.

Thanks to bug reports from 

Yar Odin
Michael Cramer
Sridhar Komandur
Heddy Boubaker
Mitar
Sergey Mokryshev
Günter Knaf
