fix USING_PART_OF_NAMESPACE_EIGEN to export ei_ prefixed math functions
fix USING_PART_OF_NAMESPACE_EIGEN to export ei_ prefixed math functions

cjntaylor/eigen,cjntaylor/eigen,pthulhu/eigen,pthulhu/eigen,cjntaylor/eigen,pthulhu/eigen,pthulhu/eigen,pthulhu/eigen,cjntaylor/eigen