- bug (712/716): why did this happen? probably block split went amok.

shell_blocks_dump_activate:1552: blocks for track 0
blocklist_dump:721: blocks:
   0:       8542 [      8542] 0x40ff0bcc
   fr                       0/     17084(     17084) 0x58084b50 
   gr                       0/       268(       268) 0x58084a20 
   1:      41310 [     32768] 0x8143520
   fr                       0/     65536(     65536) 0x58070718 
   gr                       0/      1024(      1024) 0x580702f0 
   2:      64098 [     22788] 0x40ff0bf0
   fr                       0/     45576(     45576) 0x40f8aae8 
   gr                       0/       712(       716) 0x40f8a6e0 
   3:      96866 [     32768] 0x81434d8
   fr                       0/     65536(     65536) 0x40f7a6b8 
   gr                       0/      1024(      1024) 0x58052590 
   4:     129634 [     32768] 0x40ff0c08
   fr                       0/     65536(     65536) 0x5809e7d0 
   gr                       0/      1024(      1024) 0x40f7a290 
   5:     159680 [     30046] 0x40ff0bfc
   fr                       0/     60092(     60092) 0x5808e7c8 
   gr                       0/       940(       940) 0x40f32318 

- make selection independant per track (ui is problematic) (maybe).
- fix block_join and use it.
- start play while loading yields incorrect (too low) frame_count
  so that playing stops prematurely. (not a bug, just inconvenient)
- correctly "blend" graph data on element boundaries.
- reentrancy issues when nesting actions.
- disable certain functions on save, clipboard, etcetera.
  (i.e. reentrancy above)
- selection control & undo is fragile. (not very important)
- proper locking between player and gui threads particularly
  wrt. to recording. (basically done, maybe bugs)
- more efficient replace operation (currently delete/insert).
- optimize redrawing, blit new data only.
- better display algorithm for low magnification.
- show clipboard. (sort of done, still problems, i.e. markers/selection
  are lost when opening/closing clipboard)
- multiple clipboards.
- clean up actions and stuff.
- redo after undo.
- disk store for clipboard and undo buffers at least.
- sample format conversion on output.
- mixer routing controls.
- select + drag outside window should scroll.
- error handling + reporting (e.g. word wrap).
- track down does not work on 4 channels (done)
- fade broken again. (done)
