Bug#953116: libpetsc-complex: compile PETSc with --with-64-bit-indices

[Drew Parsons]

Source: petsc
Followup-For: Bug #953116

Nice bug.  There are ramifications for upgrading all pointers to 64
bit.  Probably we don't want to do that without being explicit about
it.  64 bit pointers should be enabled right through the computational
library stack, or there will be a mismatch at some point causing
failure.

This ties in with developments of the BLAS packages. These now have 64
bit variants (libblas64-dev etc).  

BLAS is at the bottom of the stack, 64 bit pointers need to be
activated each step of the way upwards. Need to check 64-bit PETSc is
consistent with scalapack and MUMPS, for instance.