pv->pvn for literals in pp_require and Perl_sv_derived_from_pvn

pv->pvn for literals in pp_require and Perl_sv_derived_from_pvn

I found these 2 strlens while stepping through the interp while running a
script and both came from a pp_require. UNIVERSAL::can was not modified
since it is more rarely called than pp_require. A better more through
investigation of version obj comparison and upgrading will need to be done
in the future (new funcs needed for the derived/upg_version idiom, remove
the upg_version since it was changed to always be a ver obj, etc).