[petsc-dev] --download and spack

[Jed Brown]

We're currently maintaining a (somewhat clumsy and limited, albeit
functional) package manager in the form of the --download functionality.
What do people think of outsourcing this to Spack, which would handle
dependency resolution and report includes/libraries to PETSc?  That
would enable reuse of installed packages between different PETSC_ARCH
and be more reliable regarding upgrade/downgrade when switching
branches.