It is not enough to to initialize temporary vectors via the

constructor that just takes the size argument as this neglects the
structure of the values. I. e. if the values of a block vector are
block vectors itself there was no space allocated and thus the solvers
segfaulted.

In case of CGSolver this fixes Flyspray task #81
<http://hal.iwr.uni-heidelberg.de/flyspray/index.php?id=81&do=details>.

It will not be closed as I want to write some tests for the ISTL
kernels as this bug is likely to occur at other places as well.

[[Imported from SVN: r490]]