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Until now we were defining errors like this:

    const error ErrSomething  = errors::New("abc");

However there is a problem here: the runtime will call ErrSomething
destructor on program exit, and for refptr<T> the destructor does 2
things: a) decrefs the object, and b) switches embedded pointer to NULL;

If another thread is still running both "a" and "b" can become race
conditions if that T2 uses ErrSomething via e.g. just

    ...
    if (err == ErrSomething)
        ...

Here is, for example TSAN report about ErrPyStopped usage when accessed by timer thread:

    WARNING: ThreadSanitizer: data race (pid=4224)
     Read of size 8 at 0x7f0d6840e150 by thread T92:
       #0 golang::refptr<golang::_error>::refptr(golang::refptr<golang::_error> const&) golang/libgolang.h:525 (liblibpyxruntime.so.0.1+0x4edc)
       #1 golang::pyx::runtime::PyFunc::operator()() const golang/runtime/libpyxruntime.cpp:222 (liblibpyxruntime....