Add <esc>-^L for local repaint, fix minor escape-key bugs

This adds <escape>-^L as a way to repaint the client's screen without involving the server.  It also makes prediction work more correctly on escape-key sequences, not that it matters a whole lot.  This resolves #370.

Additionally, I think the repaint-on-normal-^L is kind of a bad idea, but I haven't done anything about that here.