Rename preprocessor symbol used to activate server-crash for testing.

* subversion/libsvn_repos/repos.c (get_repos): Make crash dependent on
   SVN_DEBUG_CRASH_AT_REPOS_OPEN instead of SVN_DEBUG.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1432137 13f79535-47bb-0310-9956-ffa450edef68