Long prompts interfere with display of readline search

[melvinw]

Mostly opening this so I can remember to fix this if I can't come up with a fix before I get distracted...

This is most easily demonstrated in this screencast: https://asciinema.org/a/BPyNDjxbRoJ0Kd7F3jSzFflRx

Basically, when PS1 is long, the buffer while doing a ctrl+r search looks wonky. This doesn't happen in bash.

You can reproduce by opening two shells. One with PS1='\u@\h:\w\$ ' and another with the default or something minimal like PS1='\$ '. Press ctrl+r in both and note that, in the first shell, some garbage text from the trailing portion of the prompt that doesn't overlap with (reverse-i-search)':` lingers until you end the search.

[melvinw]

Oh nice. It looks like someone else opened a bug (#2081) for this back in September. I'll use that instead.