Safe string handling with config-load error messages

We were just trusting that the error strings would be shorter than 256 (usually), but since we're including paths and strerror() results, we really have no control over the length of the error strings. So enforce some healthy boundaries. This could explain the crashes that Divarin of Mutiny is seeing with SCFG on WinXP or maybe it was the truncsp(strerror()) stuff that was just removed as well. We'll see...