Fix a few security problems. Avoid problems with pipes, sockets, etc. in

the filesystem.  Use sub_req_lookup_file for various functions that
open ancillary files, so that they have to pass the symlink tests.  Also
disallow slashes in HeaderName and ReadmeName to avoid ../../../hacks.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@78357 13f79535-47bb-0310-9956-ffa450edef68