Add a path to the DocBook XSL Stylesheets search path

Slackware puts the stylesheets in /usr/share/xml/docbook/xsl-stylesheets*
Patch from Andrea Rossato.

configure.ac

@@ -929,7 +929,7 @@ AC_PATH_PROGS(TarCmd,gtar tar,tar)
 
 dnl ** check for DocBook toolchain
 FP_CHECK_DOCBOOK_DTD
-FP_DIR_DOCBOOK_XSL([/usr/share/xml/docbook/stylesheet/nwalsh/current /usr/share/xml/docbook/stylesheet/nwalsh /usr/share/sgml/docbook/docbook-xsl-stylesheets* /usr/share/sgml/docbook/xsl-stylesheets* /opt/kde?/share/apps/ksgmltools2/docbook/xsl /usr/share/docbook-xsl /usr/share/sgml/docbkxsl /usr/local/share/xsl/docbook /sw/share/xml/xsl/docbook-xsl /opt/local/share/xsl/docbook-xsl])
+FP_DIR_DOCBOOK_XSL([/usr/share/xml/docbook/stylesheet/nwalsh/current /usr/share/xml/docbook/stylesheet/nwalsh /usr/share/xml/docbook/xsl-stylesheets* /usr/share/sgml/docbook/docbook-xsl-stylesheets* /usr/share/sgml/docbook/xsl-stylesheets* /opt/kde?/share/apps/ksgmltools2/docbook/xsl /usr/share/docbook-xsl /usr/share/sgml/docbkxsl /usr/local/share/xsl/docbook /sw/share/xml/xsl/docbook-xsl /opt/local/share/xsl/docbook-xsl])
 FP_PROG_FO_PROCESSOR
 
 dnl ** check for ghc-pkg command