B::INVLIST isa B::PV (for now)

If the compiler stumbles over a B::INVLIST treat it as B::PV
and do not error.
Also restore rudimentary B versioning support for BIND and INVLIST.
mg.h: Suppress compiler warning

GCC says:
pp_hot.c: In function 'Perl_pp_match':
pp_hot.c:1453: warning: signed and unsigned type in conditional expression