Adjust to the moving target called the C++ standard. Apparently nowadays it's not allowed to define an explicit copy constructor but not an assignment operator. Consequently, defining the explicit copy constructor in terms of the implicit/automatic assignment operator for general convenience no longer works. Add assignment operators. Caution: not tested with the IBM compiler, but there's no particular reason it shouldn't work.

assertion "csx < csmax" failed: file "../../../src/oldclasslib/include/charsink.h", line 162, function "virtual character_sink& string_accumulator::operator<<(int)"
[1]   Abort trap              ../../examples/m...
Exit 134