Got rid of the hlink_pool in favor of using the new hashtable code

Got rid of the hlink_pool in favor of using the new hashtable code
on the receiving side.  This allows us to always use a 32-bit number
to identify the hardlink clusters, even on a system where pointers
are 64-bits.  Also made changes to handle the use of F_ROOTDIR() and
F_DEPTH() instead of the old union that wasted space on the
receiving side when pointers are 64-bits.