Request: safe inet_ntop() usage and increase number of tries.

This patch makes the inet_ntop() function behave safe allocating
a new memory space when processing replies on one thread. It
also instruct the RDNS resolver to perform multiple retries in case
some of them timeout due to slow responses from DNS backends or any
delay caused by PHP module.

The patch have been tested with NginX + PHP5-FPM on Ubuntu 14.04. Without
this fix, the requests may fail 8/20. The patched version runs 20/20.

Note: this needs more testing from a production environment.

Signed-off-by: Eduardo Siva <eduardo@monkey.io>