Start svnserve as daemon from the swig-ruby tests on Windows.

This ugly hack (which could really use some cleanup from somebody with more
ruby interests than me), fixes +- 70 tests on the buildbot, by removing a
running as administrator requirement.

This hack assumes that the buildbot kills svnserve before the next build
(which happens to be the case on our Windows buildbots).

* subversion/bindings/swig/ruby/test/windows_util.rb
  (Svnserve): Replace one ugly hack that starts svnserve, with a different
    hack that at least works with reduced privileges.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1518238 13f79535-47bb-0310-9956-ffa450edef68