maint: address syntax-check errors.

* cfg.mk: Ignore the "error" call in tests/c++.at, it is not to be
translated.
* doc/bison.texi: Fix incorrect @pxref use.
* po/POTFILES.in: Add missing file.
* src/print_graph.c: Remove useless include.

po/POTFILES.in

@@ -9,6 +9,7 @@ src/main.c
 src/muscle-tab.c
 src/parse-gram.y
 src/print.c
+src/print_graph.c
 src/reader.c
 src/reduce.c
 src/scan-code.l