ap_os_is_filename_valid() has been added to Win32

to detect and prevent access to special DOS device file names.

Submitted by:	Paul Sutton, Ken Parzygnat
Reviewed by:	Roy Fielding


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@82603 13f79535-47bb-0310-9956-ffa450edef68