genpacksizetables.pl: Correct comment typo
Propagate a change from commit 1651fc447620d361 into genpacksizetables.pl.

pp_pack.c contains a table generated by genpacksizetables.pl, pasted into the
C source. The C source was updated by commit 1651fc447620d361 in April 2007,
but the table used to generate the code was not.
Extract the generated packprops array into packsizetables.c.

The C source is the output from genpacksizetables.pl
Previously it was pasted into pp_pack.c

 LocalWords:  packprops
Refactor genpacksizetables.pl to use regen/regen_lib.pl
Move genpacksizetables.pl to regen/genpacksizetables.pl
Add regen/genpacksizetables.pl to t/porting/regen.t
Merge the reworking of how genpacksizetables.pl is used.