On the fsfs-format7 branch: fix bug that prevented efficient encoding
of negative values.

* subversion/libsvn_subr/packed_data.c
  (svn_packed__data_flush_buffer): use signed type to detect negative values

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1463120 13f79535-47bb-0310-9956-ffa450edef68