Make sure FSX builds with older versions of APR as well by
including our dependency compatibility header.

* subversion/libsvn_fs_x/index.c,
  subversion/libsvn_fs_x/noderevs.c,
  subversion/libsvn_fs_x/string_table.c
  (): #include svn_dep_compat.h


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1509950 13f79535-47bb-0310-9956-ffa450edef68