Bug#1065323: petsc: bad Provides in libpetsc64-real3.19t64, libpetsc64-complex3.19t64 and libpetsc-real3.19t64

[Drew Parsons]

Source: petsc
Followup-For: Bug #1065323

petsc has a complex set of symlink farms since it needs to enable
multiple alternative build profiles.

I'll implement the patch in a way that doesn't let t64 get in the way
of updating subsequently (to 3.20 in the near future).

Drew