Add IPv6 support to check_fping
This patch adds command line options -4 and -6 (--use-ipv4 and --use-ipv6) to check_fping. IPv4 is used by default, maintaining backwards compatibilty with older check_fping versions. IPv6 support requires the fping6 program.
The implementation is really an imitation of check_ping IPv6 support: Plugin command line option -4/-6 designates whether to run fping/fping6.
Please note that especially the changes to configure.in might be all wrong - I don't know what's the proper autoconf way, patching configure.in just seemed to work for me.
Patch against Plugin Version (-V output): Git master on 2012-02-21
Plugin Name: check_fping
Example Plugin Commandline: check_fping -6 -H ping.funet.fi
Tested on operating system: Ubuntu 11.10 Oneiric
Tested on architecture: x86_64
Tested with compiler: gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3)