Cherry-pick commits to the release branch

d3b0b70 (Matthias Maier, 15 minutes ago)
   port other tests to new macro

6c9a594 (Matthias Maier, 26 minutes ago)
   Test umfpack/umfpack_04: Avoid printing exact number of iterations

   This commit introduces a new macro for tests to test an iterative solve to
   convergence within a given number of iteration steps. Due to roundoff
   errors the exact number doesn't have to be stable...

423d98e (Matthias Maier, 55 minutes ago)
   Test bits/step-51: Improve output

   This allows numdiff to catch small roundoff errors.

c42682a (Martin Kronbichler, 4 hours ago)
   Fix constructor of SchurMatrix for 64 bit indices.

da05d8c (Martin Kronbichler, 25 hours ago)
   Fix bug in Trilinos SparseMatrix::add/copy_from

   We assume that the pointers to a Trilinos sparse matrix remain valid when a
   matrix is copied from another one or added and the two matrices share the
   same sparsity pattern. This is used in step-32. However, the fix introduced
   in 8d64256 could not ensure this
   (while fixing a few other cases). The check if the two sparsity patterns
   point to the same memory is not good (we can have the same sparsity pattern
   memory but different addresses).

   Therefore, the add and copy_from methods need to be more careful to not set
   up a new matrix structure when this is not necessary. In particular, the
   two methods now check whether the column indices are the same in any case
   but without requiring calling methods that change the memory layout.