Fix located_block's token memory leak (revisit with better solution)
Fix located_block's token memory leak (revisit with better solution)

_hdfs_located_block_new_proto() first calls hdfs_located_block_new(),
which allocates _token with hdfs_token_new_empty(), but then reassigns
_token with _hdfs_token_new_proto().

This short term fix frees _token between the _new_empty() and
_new_proto() calls to prevent a memory leak, but this allocation just
to immediately free is wasteful, so change this to something smarter

cemeyer/hadoofus,cemeyer/hadoofus