CFR: add an example of manually fetching distfiles to Porter's Handbook

[Mark Linimon]

A few people are getting "creative" again on ways to express this common
need.  AFAIK the following is the best way to do it.  What do people think?

mcl

Index: book.sgml
===================================================================
RCS file: /home/FreeBSD/dcvs/doc/en_US.ISO8859-1/books/porters-handbook/book.sgml,v
retrieving revision 1.1119
diff -u -r1.1119 book.sgml
--- book.sgml	4 Nov 2011 14:28:43 -0000	1.1119
+++ book.sgml	1 Dec 2011 22:26:38 -0000
@@ -4698,6 +4698,19 @@
 	  <filename>/usr/ports/LEGAL</filename> for every listed distribution
 	  file, describing exactly what the restriction entails.</para>
       </sect2>
+
+      <sect2>
+	<title>Examples</title>
+
+	<para>The preferred way to state "the distfiles for this port must be
+	  fetched manually" is as follows:<programlisting>
+.if !exists(${DISTDIR}/${DISTNAME}${EXTRACT_SUFX})
+IGNORE=         "may not be redistributed because of licensing reasons. Please visit <replaceable>some-website</replaceable> to accept their license and download ${DISTFILES} into ${DISTDIR}"
+.endif</programlisting></para>
+
+	<para>This both informs the user, and sets the proper metadata on
+	  the user's machine for use by automated programs.</para>
+      </sect2>
     </sect1>
 
     <sect1 id="building">

mcl