Remove expired ports:
2016-09-30 math/why3-spark: Only useful for deprecated lang/spark
2016-09-30 lang/spark: Broken for more than 6 months
2016-09-30 math/alt-ergo-spark: Only useful for deprecate lang/spark
2016-09-30 security/nessus-libnasl: Abandoned, consider using OpenVAS
2016-09-30 security/nessus: Abandoned, consider using OpenVAS
2016-09-30 security/nessus-libraries: Abandoned, consider using OpenVAS
2016-09-30 security/nessus-plugins: Abandoned, consider using OpenVAS

Drop spark-related ports for removal after 30 Sept

Remove ${PORTSDIR}/ from dependencies, categories m, n, o, and p.

With hat:	portmgr
Sponsored by:	Absolight

Add new port math/alt-ergo-spark (required by SPARK 2015)

This will be RUN_DEPENDS for lang/spark when it is fixed.  The "stock"
math/alt-ergo cannot be used, it locks up when gnatprove calls it.