Support freezing multiple repositories in libsvn_repos and
make svnadmin support both:

  svnadmin freeze repository command arguments...
  svnadmin freeze -F file_of_repositories command arguments...

* subversion/include/svn_repos.h
  (svn_repos_freeze): Change parameter to array.

* subversion/libsvn_repos/repos.c
  (struct freeze_baton_t): New.
  (multi_freeze): New.
  (svn_repos_freeze): Change parameter to array, call multi_freeze.

* subversion/svnadmin/svnadmin.c
  (options_table): Add -F.
  (cmd_table): Add -F to freeze.
  (subcommand_freeze): Handle one repository or a file of repositories.
  (sub_main): Parse -F, don't expect explict repository with -F.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1446504 13f79535-47bb-0310-9956-ffa450edef68