reinstate cpan/IO-Compress/Makefile.PL

This was removed a year ago, but it causes problems with
ABSTACT and ABSTACT_FROM; since there isn't an IO/Compress.pm
file. make_ext.pl special-cases Makefile.PL to get the abstract
from IO/Compress/Base.pm; but MakeMaker looks for, and fails to
find, 'IO::Compress - ...' in the pod for that file,and prints an error.

Rather than more special-casing, it's easier to just restore the
distribution's Makefile.PL, which already contains the correct
'ABSTRACT => ...' entry.
special-case Pod::Checker ABSTRACT

Currently the auto-generated Makefile.PL for Pod::Checker raises a
warning with MakeMaker, since the abstract in the pod isn't parseable.

Also, the package's own Makefile.PL doesn't work with blead (I didn't
exactly understand what the issue was, but porting/dual_lift.t complained
about missing utilities).

So the most expedient hack is to special-case the ABSTRACT in make_ext.pl.