Stop on error: repeat last two words instead of last word

[glibg10b]

I propose adding a "two words" option to "stop on error":

After typing a word, some fingers start moving to prepare for the next word. If a finger moves incorrectly, a typo occurs in the next word. When re-typing the word, we don't practice fixing this mistake because we skip the transition that made it happen in the first place. This transition differs depending on the end of the previous word, so we should start with that word.

See #4315 for an example.