Compile with -Wcast-qual.

Compile with -Wcast-qual.

That let me find what might have been the bulk of the 579(!) instances
of "Deconst" reported in

    http://www.cl.cam.ac.uk/~dc552/papers/asplos15-memory-safe-c.pdf

and, hopefully, will prevent more from creeping in.

There are some remaining ones - and they represent attempts to overwrite
the packet bytes handed to tcpdump by libpcap, which could well *fail*
with, for example, memory-mapped capture mechanisms!