[PATCH] Don't allow a backslash in a path component (CVE-2006-1863)

Unless Posix paths have been negotiated, the backslash, "\", is not a valid
character in a path component.

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>