textproc/libxslt depending on libxml >= 2.6.15

[Linus Nordberg]

# $FreeBSD: ports/textproc/libxslt/Makefile,v 1.68 2004/10/29 18:58:25 marcus Exp $
fails.
>From config.log:
configure:22284: checking for libxml libraries >= 2.6.15
configure:22343: error: Version 2.6.13 found. You need at least libxml2 2.6.15 for this version of libxslt

(Makefile rev. 1.69 is current but it fixes a libcrypt dependency only.)

Regards,
Linus