- The `dump_stack()` method could call a `__repr__` method implemented in Python,
causing (infinite) recursion.
I rewrote it to only print out the values for some fundamental types (`int`, `str`, etc.);
for everything else it just prints `<type_name @ 0xdeadbeef>`.
- The lltrace-like feature for uops wrote to `stderr`, while the one in `ceval.c` writes to `stdout`;
I changed the uops to write to stdout as well.