update matio library to latest head (git://matio.git.sourceforge.net/gitroot/matio/matio, 7af9e767f450e8cc54c5ecf1f80ed7a7a9b273de)

git-svn-id: https://svn.modelica.org/projects/Modelica/trunk@7594 7ce873d0-865f-4ce7-a662-4bb36ea78beb