Obtain afs status items directly from afs.

Obtain afs status items directly from afs.

This patch changes the way how the afs status items are passed from afs to the stat
command handler. Previously, afs passed the status item string to the server process
whenever a new audio file was loaded. The server process stored the string in the mmd
shared memory area from which it was available to the client process that executed the
stat command.

This approach has the disadvantage that  the size of the string must be restricted to a
fixed number of bytes,  VERBOSE_LS_OUTPUT_SIZE, determined at compile time and
independent of the audio file.  As version 2 id3 tags and vorbis comments do not impose
an upper bound on the size of the tags a rather ugly patch was merged recently to the master
branch which truncated the size of the tags if it exceeded VERBOSE_LS_OUTPUT_SIZE.

This patch gets rid of this restriction by not storing the info string in the mmd structure. Instead,
the stat command requests the information directly from the afs process via the callback
mechanism which is also used by other afs commands.