Following up on r1592717, process 'svnadmin dump' output as binary instead of
text. This resolves a Windows test failure in a test for eol handling in
properties.

* subversion/tests/cmdline/svntest/main.py
  (run_svnadmin): Detect when to return output as binary vs as text.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1592987 13f79535-47bb-0310-9956-ffa450edef68