Make some mergeinfo tests pass against old servers.
* subversion/tests/cmdline/mergeinfo_tests.py
(adjust_error_for_server_version): Add a .* to the beginning (which
is done automatically by run_and_verify_mergeinfo but not
run_and_verify_svn which is used by mergeinfo_on_unknown_url).
(mergeinfo_on_unknown_url): Adjust error for server version.
(test_list): Only XFail explicit_mergeinfo_source for servers with
mergeinfo.
git-svn-id: http://svn.collab.net/repos/svn/trunk@30469 612f8ebc-c883-4be0-9ee0-a4e9ef946e3a