[3067] Detect if elinks exists before trying to use it to generate docs

configure.ac

@@ -1132,6 +1132,11 @@ if test "x$enable_generate_docs" != xno ; then
     fi
     AC_MSG_RESULT(yes)
   fi
+
+  AC_PATH_PROG([ELINKS], [elinks])
+  if test -z "$ELINKS"; then
+    AC_MSG_ERROR("elinks not found; it is required for --enable-generate-docs")
+  fi
 fi
 
 

doc/guide/Makefile.am

@@ -21,10 +21,8 @@ bind10-guide.html: bind10-guide.xml
 		http://docbook.sourceforge.net/release/xsl/current/html/docbook.xsl \
 		$(srcdir)/bind10-guide.xml
 
-HTML2TXT = elinks -dump -no-numbering -no-references
-
 bind10-guide.txt: bind10-guide.html
-	$(HTML2TXT) bind10-guide.html > $@
+	@ELINKS@ -dump -no-numbering -no-references bind10-guide.html > $@
 
 bind10-messages.html: bind10-messages.xml
 	@XSLTPROC@ --novalid --xinclude --nonet \