In Search dialog in mcedit M-n hotkey was used for normal search mode.
Therefore, M-n as HistoryPrev in the input line was in accessible.
Change hotkey for normal seach mode to M-r. Use this hotkey for normal diff
mode in mcdiffviewer to unify i18n resources.
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>