Create a new test file for dump/load tests in the libsvn_repos test suite.

The all-in-one 'repos-test.c' file has grown rather large and I added the
first dump/load-related test to it only recently and I want to add more.

* build.conf
  (dump-load-test): New section.
  (__ALL_TESTS__): Add 'dump-load-test'.

* subversion/tests/libsvn_repos/repos-test.c
  (test_funcs): Remove 'test_dump_r0_mergeinfo'.
  (dump_r0_mergeinfo_notifier, test_dump_r0_mergeinfo): Move to ...

* subversion/tests/libsvn_repos/dump-load-test.c
  ... this new file.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1585931 13f79535-47bb-0310-9956-ffa450edef68