STDCXX-1058 * src/iostore.cpp (_C_copyfmt): _C_usr->_C_iarray, _C_usr->_C_isize, _C_usr->_C_parray, _C_usr->_C_psize, _C_usr->_C_cbarray, _C_usr->_C_cbsize set to zero after deletion. * tests/regress/27.basic_ios.copyfmt.stdcxx-1058.cpp: added regression test.