KMessageBox: Set very long lines to wrap, even on very wide screens

Monitors are getting ever wider. The old heuristic to wrap when exceeding half the screen width is no longer good enough, and still allows ridiculously wide non-wrapped messageboxes.

This patch adds wrapping at around 70 characters. That limit is somewhat arbitrarily chosen, but certainly not too low, IMO. It is based on a translated string, such as to be adjustable to what makes most sense in a language's charset.