e-added port: science/PETSc: Suite of data structures and routines from Argonne National Laboratory (existed 2004/11/21-2014/09/01, deleted in r366959)
Replacing the identical version committed by me as a new port in r456696.
The old math/petsc port also had a slave port math/petsc-mpich that has also been deleted.
Original differential revision is https://reviews.freebsd.org/D13527
Submitted by: myself
Reported by: thierry that math/petsc and math/petsc-mpich existed before
Approved by: adamw (mentor)