Bug#989550: suitesparse: enhance 64-bit support in suitesparse

[Drew Parsons]

Package: suitesparse
Followup-For: Bug #989550

libcholmod3 and libspqr2 and libumfpack5 seem to be the only
SuiteSparse components directly affected by the 64-bit numerical
library stack, by linking to libblas.so.3 and liblapack.so.3.
libcholmod3 also links to libmetis5, and libspqr2 and libumfpack5
link to libcholmod3.

Not sure if this makes the packaging easier or harder.
Should libspqr64-2 link to libamd64-2 or to libamd2 ?
Should libamd64-2 be provided if it's identical to libamd2 ?