C: special-case (bytes|utf8)_heavy, force compile-time inclusion

added sub force_heavy. monkey-patch ::AUTOLOAD to omit a Carp dependency.
not needed for Carp::Heavy, Exporter::Heavy, as they are included properly
by package deps.

added t/issue185.t

WIP: 185 and 235 failing, t/testc.sh -q -O3 81 174 185 224 235 255