Store revision values in FSX change lists containers as signed integers
instead of unsigned ones.

* subversion/libsvn_fs_x/changes.c
  (svn_fs_x__write_changes_container,
   svn_fs_x__read_changes_container): use "int" instead of "uint" for revs

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1543623 13f79535-47bb-0310-9956-ffa450edef68