When a reference counter is at its limit, don't allocate a new
TagPoolSlot - that would result in many TagPoolSlot instances with
ref==1.  This in turn would make the linked list very very large,
which means quadratic runtime for many operations.

Fixes deadlock.

Prepare for APE tag support on userspace NFS/SMB/CIFS mounts.

Prepare for ID3 support on userspace NFS/SMB/CIFS mounts.

Use a 128 byte buffer instead of reading 10 bytes first and then 118.

Copy the query buffer to the allocated buffer, and read only the
remaining data.

Omit the file size check if we don't know the size.

Apply padding only to the fseek(), not to the chunk size.  This fixes
bogus "failed to read riff chunk" messages when the last chunk has an
odd size.

See http://bugs.musicpd.org/view.php?id=4486