exonerate-server: set the listen() backlog to the value specified by the
--maxconnections parameter to increase the likelihood of the server being
able to service that many concurrent connections. Previously, the backlog
was hard-coded to 5 (per "The Linux Programming Interface" by Michael
Kerrisk: "In the original BSD sockets implementation, the upper limit for
backlog was 5, and we may see this number specified in older code"). This
caused the exonerate-server to not accept > 8 connections on FreeBSD, and
the exonerate clients would core dump when compiled with
"--enable-assertions".