QCompleter previously replaced the entire search bar text when
accepting a suggestion, wiping all previous tags. Added _TagCompleter
subclass that overrides splitPath (match against last tag only) and
pathFromIndex (prepend existing tags). Accepting a suggestion now
replaces only the last tag.
Space clears the suggestion popup so stale completions from the
previous tag don't linger when starting a new tag.
behavior change: autocomplete preserves existing tags in multi-tag
search; suggestions reset on space.
pax
a8dfff90c5