On the fsx branch:  List fsx as available in 'svnadmin help create'
and put a big warning sign on it

* subversion/svnadmin/svnadmin.c
  (options_table): mention and warn about 'fsx' for svnadmin__fs_type

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx@1509255 13f79535-47bb-0310-9956-ffa450edef68