Follow up to r1464985 and r1465170, merge the two approaches to warning about
BDB deprecation.

* subversion/svnadmin/svnadmin.c (subcommand_open): Update comment and
   print warning directly to stderr without creating an svn_error_t first.
* subversion/tests/cmdline/svntest/main.py (create_repos):
   Adjust expected output and rename some local variables.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1465268 13f79535-47bb-0310-9956-ffa450edef68