Generate the table of core magic types in perlguts.pod using mg_vtable.pl

Generate the table of core magic types in perlguts.pod using mg_vtable.pl

This fixes a couple of errors and omissions, and resorts the table in the same
case insensitive order as the header files. It eliminates 1 overlong verbatim
line of pod.

As there's no good way to include component files into the core pods, and the
regen scripts aren't designed to modify in place, generate this to STDOUT (if
-g is added to the command line), to be hand edited into place. It would be
nice to be able to automate this fully.