[LAU] Snd learning curve

[Bill Schottstaedt]

The "cursor-moves-while-playing" flag is with-tracking-cursor.  It defaults
to false currently -- perhaps I should change that.  You can set it in the
preferences dialog (under "Cursor", "track current location while playing"),
or via (set! (with-tracking-cursor) #t). I've used about a half dozen names
for this over the years -- the word "track" has so many meanings in computer 
music that I have tried to avoid it.

I've added an easy way to play the selection looped (in the current
daily tarball or the CVS sources).  In older versions, if you have the 
context-sensitive menus loaded, right click in the selection, and choose 
"Loop play". Otherwise you need to run the code that performs that operation
(see popup.scm).  But as I say, it's easier now in the new Snd version.
There's also an arrow for "play from the cursor".

The preferences dialog complaint that a module isn't loaded is harder
to fix because you can run different versions of Snd, and the dialog
is tailored to whatever is currently loaded, but saves the preferences
in some file like ~/.snd_prefs_s7 which is loaded by any version.  The complaint itself
arises because you're asking for some feature that depends on a
module (the Gtk/Motif bindings for example) that isn't loaded in the
Snd you're currently running, and that can't be found as a run-time loadable
library. I think I'll change the dialog to provide settings only for stuff 
that is always available.  (And I'll move a lot of that stuff into the basic
Snd).