r2632: a new approach to handling const errors. We have had huge numbers of

r2632: a new approach to handling const errors. We have had huge numbers of
const warnings for a long time, and no real way to approach a
solution. Some of them are unavoidable due to the way the C standard
works (for example, any function that provides strchr() like
functionality _must_ produce a const warning)

I will be converting a bunch of places that currently produce const
warnings to use the discard_const_p(). Some of these will be
unavoidable const problems, some of them will be ones we will fix up
over time. At least this change means we will no longer be swamped
with const warnings, and we will easily be able to see when new
problems emerge.
(This used to be commit fec3288ad6ce58e8273e3f16e88037db49ecf046)