fix binding name for set-tempo-from-region
back port 6576105 from cairocanvas as fix for data loss/file deletion
substantive changes to the logic and safety for naming of (audio/MIDI) sources, especially when created via import
fix crash recovery: add new constructors to SndFileSource, AudioFileSource, add a new SourceFactory method and finally tweak
AudioDiskstream::use_pending_capture_data() to create both the required whole-file and the in-playlist regions