[PATCH] Policy Enforcement: config.h or squid.h includes

We currently have a policy that config.h MUST be included first so as to
pull in the portability definitions early. It MAY be included via the
legacy squid.h at present.

This alteration to the source maintenance script validates that each .c
and .cc file in the sources includes config.h or squid.h first in its
include order.

  * an ERROR: line is produces for each violating file
  * as yet the maintenance run is not blocked so as to catch as many
errors as possible in one run.
  * as yet there are no related code alterations performed by this
script. It only validates.
  * trace FORMAT: informative lines are silenced to make ERROR: more
visible.

Unless there are objections I'll commit immediately.

(see other Cleanup patch for fixes of the problems this already detects).

Amos