Drag'n'drop from Folders into a playlist/auto-dj does not work

Confirmed with latest trunk on OSX X 10.6.8

For example when dropping 2 tracks fron FInder into AutoDJ:

Debug [Main]: Committing transaction on "qt_sql_default_connection" result: true
Debug [Main]: TrackDAO(0x1060b4dc0) addTracks took 6 ms to add 2 tracks
Debug [Main]: BaseTrackCache(0x119621420) updateIndexWithQuery took 0 ms
Debug [Main]: src/library/dao/playlistdao.cpp 435 FAILED QUERY [ "UPDATE PlaylistTracks SET position=position+1 WHERE position>=1 ANDplaylist_id=2" ] QSqlError(-1, "Unable to fetch row", "No query")
Debug [Main]: src/library/dao/playlistdao.cpp 435 FAILED QUERY [ "UPDATE PlaylistTracks SET position=position+1 WHERE position>=1 ANDplaylist_id=2" ] QSqlError(-1, "Unable to fetch row", "No query")
Debug [Main]: Committing transaction on "qt_sql_default_connection" result: true

I've had the error on Windows/Linux for 1.11-a/1.10/1.09

Ok I've did some triaging today. wTrackTableView::dropEvent() works almost fine(more on that in p.s.)
PlaylistTablemodel::addTracks() seems to works fine the problems lies in playlistdao.
PTM calls trackdao.addTracks first and this works fine but the call to playlistdao.addtracks afterwards fails and returns 0 added tracks, it does not matter if the track is already in the library or not.

p.s. I found these two comments on wtracktableview.cpp

TODO: Filter out invalid URLs (eg. files that aren't supported audio filetypes, etc.)
// XXX: Crappy, assumes all URLs are valid songs. Should filter
              // out invalid URLs at the start of this function.

select() happens only for crates, adding select() in LTM::addTracks() should fix this.

The error was just a missing space character.

The patch also takes care of the TODO in wtracktableview.cpp. I'm not sure if this is really necessary since we don't accept drop events for files that aren't audio files anyway.

The rest is some reformatting to follow the coding guidelines.

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/6529