Modify pt-mat.cc to solve a problem related to vertcat/horzcat overloading. * pt-mat.cc (tm_row_const::tm_row_const_rep::init): Do not check dimension consistency when at least one of the elements is an object (this was preventing horzcat overloading from working properly, see bug #38128). (tm_const::init): Same thing for vertical concatenation (this was preventing vertcat overloading from working properly, see bug #38128). * test/classes/classes.tst: Add tests for the vertical and horizontal concatenation of objects when neither vertcat() nor horzcat() is overloaded.