multi-line entries in history cause erroneous behavior

[knz]

Found with the following:

1. enter a multi-line entry in the history (e.g. AddHistory("foo\nbar"))
2. recall the multi-line entry. The cursor is positioned (correctly) at the end of the last line.
3. try to navigate backwards with left-arrow: the display is messed up.

[knz]

Note: you need to use xterm, st or some more strict vt100 terminal emulator to see this problem occurring. With OSX terminal, iTerm or tmux/screen the issue disappears.