Same buffer completer: Don't pick up on in-progress words

Also bump some limits: rescan stale after 60 seconds, and search 6
buffers by default.
Completer: Prefer case matching completion over non-case-matching
Make replace commands use wildcard inputs

Fixes pattern/replacements with spaces in them.
Editor.paste: Don't reuse newline()

Since that can trigger all sorts of funky business, and we just want
to insert the text as is.