Fix for a unit test of lib.linear_algebra.matrix_exponential.matrix_exponential().

This is for old numpy versions.
Backported the relax 3.0.1 CHANGES file addition to trunk.

The command used was:
svn merge -r21160:21161 svn+ssh://bugman@svn.gna.org/svn/relax/tags/3.0.1 .