Fix building ZipArchiveTests with boost.
Fix building ZipArchiveTests with boost.

operator= has issues with copying the auto mutex.

--HG--
branch : ogre-gsoc2013-progressive-mesh-improvements

digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre