libxml-parser-perl: fix install bug

This patch makes libxml-parser-perl behave on my system - though it looks
like it isn't necessary on all host OSses (on gentoo and opensuse it works
without, but on ubuntu lucid and Scientific 6 it fails without the patch).

Signed-off-by: Heiko Helmle <helman@gmx.net>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>