svnrdump: Handle errors the svn / svnadmin / svnauthz way.

* subversion/svnrdump/svnrdump.c
  (SVNRDUMP_ERR): Remove this macro.
  (EXIT_ERROR, SVN_INT_ERR): New macros, same as those defined in
    subversion/svn/svn.c, but for svnrdump.
  (submain): Extract most of 'main' into this new function.  Use SVN_INT_ERR /
    EXIT_ERROR to handle errors.  Remove all svn_pool_destroy calls, because
    the top-level pool is now always destroyed in 'main'.
  (main): Now just a wrapper, that creates the top-level pool, calls 'submain'
    and cleans everything up.

Patch by: Evgeny Kotkov <evgeny.kotkov{_AT_}visualsvn.com>