It took a while, but Quimup 1.3.0 is ready. Downloads are available from Sourceforge (deb32, deb64 and source).
* Added: “Drag & drop” from file manager to quimup.
* Added: “Open with” from file manager (%U or %F).
* Added: Single-instance-mode (by default).
* Added: Localization support (no translations yet).
* Added: Command line parameters (try “quimup -help”).
* Added: Rescan tags for any selection (library menu).
* Added: Folder search in the browser.
* Added: Check if mpd is running when quimup starts up.
* Added: Option to apply colors to the album info widget.
* Added: Music directory is requested from MPD (0.17+).
* Added: Playlist scrolls to drop-position after d&d.
* Added: Drop on playlist allows insert (not just append).
* Added: Manually controlled widths in library and playlist.
* Added: Track titles shown across all colums in library.
* Added: A first-run dialog with some useful tips.
* Added: More details on command line in case of MPD-errors.
* 23 bug fixes and code improvements