Add --system option to autogen.sh
Add --system option to autogen.sh

libvirt uses --system as handy shortcut to specify the standard system
locations of prefix, libdir, sysconfdir, and localstatedir. It works
so well there, we might as well have it in netcf's autogen.sh too.

hallyn/netcf,hallyn/netcf,seanbruno/fbsd-netcf,osier/netcf,emaste/netcf,seanbruno/fbsd-netcf,emaste/netcf,osier/netcf,emaste/netcf,osier/netcf,hallyn/netcf,seanbruno/fbsd-netcf