The "packed" attribute triggers a clang 4.0 warning, and it's not
necessary.  All we want is correct allocation of this
dynamically-sized struct.

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.