sci-mathematics/pari: Fix for '.' in @INC on perl 5.26 re bug #615016

sci-mathematics/pari: Fix for '.' in @INC on perl 5.26 re bug #615016

Perl 5.26 removes implied cwd from library loading paths, and
subsequently Pari's compile fails due to reliance on this implication.

These patches rectify that by constructing a library path the same
as the scripts directory, and inserting that into `@INC`

Of course, we still need the oldest pari because dev-perl/Math-Pari
needs the old version.

And of course, the files in question have minor changes over the
handful of versions, necessitating 3 *mostly* identical but slightly
different patches for the relevant versions.

I haven't filed this issue upstream, as their bug reporting stuff
looked dizzyingly confusing.

Bug: https://bugs.gentoo.org/615016
Package-Manager: Portage-2.3.6, Repoman-2.3.2