On the fsfs-format7 branch:  headers should include all required
definitions on their own.

* subversion/libsvn_fs_fs/string_table.h
  (): add missing #include

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1451740 13f79535-47bb-0310-9956-ffa450edef68