op.c:ck_subr: reify GVs based on call checker

op.c:ck_subr: reify GVs based on call checker

Instead of faking up a GV to pass to the call checker if we have a
lexical sub, just get the GV from CvGV (since that will reify the GV,
even for lexical subs), unless the call checker has not specifically
requested GVs.

For now, we assume the default call checker cannot handle non-GV sub
names, as indeed it cannot.  An imminent commit will rectify that.

The code in scope.c was getting the name hek from the proto CV (stowed
in magic on the pad name) if the CV in the pad had lost it.  Now, the
proto CV can lose it at compile time via CvGV, so that does not work
anymore.  Instead, just get it from the GV.