give back petsc (also, slepc)

[Drew Parsons <dparsons@debian.org>]

The hurd buildd got itself lost building petsc 3.7.6.  It builds fine
on the porterbox.  Please give back for building.
Once it's done, slepc should be rebuilt against it

gb petsc_3.7.6+dfsg1-2 . hurd-i386 

dw slepc_3.7.4+dfsg1-2 . hurd-i386 . -m 'libpetsc3.7.6-dev'
nmu slepc_3.7.4+dfsg1-2 . hurd-i386 . -m 'Rebuild against PETSc 3.7.6'

Thanks,
Drew