Revision 1574868

Don't let invalid mergeinfo stop 'svnadmin dump' from producing a dump.
Just continue.

Part of issue #4476 "Mergeinfo containing r0 makes svnsync and svnadmin dump
fail".

* subversion/libsvn_repos/dump.c
  (verify_mergeinfo_revisions): New function, factored out of ...
  (dump_node): ... here. And if verify_mergeinfo_revisions() produces any
    error, ignore the error and continue.

* subversion/tests/libsvn_repos/repos-test.c
  (dump_r0_mergeinfo_notifier): New function.
  (test_dump_r0_mergeinfo): New test function.
  (test_funcs): Run it.