Comment 5 for bug 890667

Actually, on second thought, it could be related to the fact that I configured igraph to use an external ARPACK implementation and not the built-in one, so no wonder that the test case fails since most (if not all) external ARPACK libraries are not thread-safe... which leads to the conclusion that we should disallow external BLAS, LAPACK or ARPACK implementations if igraph is configured in thread-safe mode.