Fix one case of win32/os2 failing to accept a UserDir c:/userdir
  argument, close a potential segfault, and accept backslashed UserDir
  path if the admin wasn't paying attention.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@87837 13f79535-47bb-0310-9956-ffa450edef68