workaround fact that R`s  DispatchOrEval() {in coerce.c`s do_anyNA()} 
fails to dispatch for "xMatrix" (even when that would be exported as class)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/matrix@2975 edb9625f-4e0d-4859-8d74-9fd3b1da38cb