Do not ignore --bin parameter for svnrdump when running Python tests.

* subversion/tests/cmdline/svntest/main.py
  (svnrdump_binary): Update obsolete comment.
  (execute_tests): Override default svnrdump path when --bin option is set.

Patch by: Evgeny Kotkov <evgeny.kotkov{_AT_}visualsvn.com>


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1548706 13f79535-47bb-0310-9956-ffa450edef68