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
C bytes_heavy: load force_heavy now in CV

in AUTOLOAD it is too late, load it when the function is requested, to be able
to replace it properly. do not need to walk the syms.
The Carp patch is not working though. bytes_heavy neither yet
t/issue235.t: adjust test 1 message

!CvCVGV_RC(cv) was only failing up to 1.42_60. afterwards it's a bytes_heavy error