Integrated --enable-docs configure switch

configure.ac

@@ -93,6 +93,23 @@ else
     CFLAGS="$CFLAGS -DDEBUG"
 fi
 
+AC_MSG_CHECKING([if we build the HTML documentation])
+AC_ARG_ENABLE(docs,
+[  --enable-docs           Use doxygen to build HTML documentation],
+[case "${enableval}" in
+  yes) build_docs=true ;;
+  no)  build_docs=false ;;
+  *) AC_MSG_ERROR(bad value ${enableval} for --enable-docs) ;;
+esac],[build_docs=false])
+
+if test "x$build_docs" = "xtrue"; then
+  AC_MSG_RESULT([yes])
+  touch doc/doc.lock
+else
+  AC_MSG_RESULT([no (use --enable-docs to enable)])
+  rm -f doc/doc.lock
+fi
+
 AC_CONFIG_FILES([
 	Makefile
 	doc/doxygen.conf