Backport suitesparse test to 2.4

This is a straightforward backport of the new SuiteSparse test from master by simply cherry-picking all commits that touched either FindSuiteSparse.cmake or FindUMFPack.cmake. On top of that, I removed the deprecation warning from the old UMFPack test and extended it to automatically populate SuiteSparse_ROOT from UMFPACK_ROOT if only the latter is set.

This fixes #14 (closed)