[CM] improvements to sndlib support

[Heinrich Taube]

svn now has some improvements to sndlib support in Grace:

1. new Autoload button lets you mark/unmark instruments for  
autoloading at start up (stored in preferences)
2. loading instruments in the Instrument Browser now handles  
instrument dependancies
3. added 'vkey.scm', a virtual sampler that uses expandn and fullmix  
with sample databases.  (the vkey-db function will set up a database  
and assign a keynumber to each sample in it automatically)
4. updated the built-in sndlib instruments to the latest  
versions,added piano.scm and animals.scm
5. new 'directory' function can be used to when building sample  
databases


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