svnrdump: Add support for subcommands
svnrdump: Add support for subcommands

* subversion/svnrdump/svnrdump.c

  (svnrdump__cmd_table): A table of subcommands along with related
  information.

  (opt_baton_t): New struct for storing options to pass around and
  dispatching subcommands.

  (help, help_cmd): Replace the help function with a new help_cmd
  function, effectively making "help" a subcommand.
  (replay_range, replay_revisions): Rename function.

  (dump_cmd, load_cmd): New functions to extract arguments from the
  apr_getopt_t and opt_baton and dispatch calls to the corresponding
  functions that do the real work. dump_cmd eventually calls
  replay_revisions, while load_cmd is currently a noop.

  (main): Replace local variables with fields in opt_baton where
  appropriate. Add logic for reading and dispatching a
  subcommand. Track changes made to other functions.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion