Missing '%' in error message raised from make_node caused SIGABRT.

Resolves: #670580
Upstream: http://www.mail-archive.com/groff-commit@gnu.org/msg00779.html

diff -uNPrp groff-1.20.1/src/roff/troff/node.cpp groff-1.20.1/src/roff/troff/node.cpp
+++ groff-1.20.1/src/roff/troff/node.cpp	2009-01-09 15:25:52.000000000 +0100
--- groff-1.20.1/src/roff/troff/node.cpp	2011-01-21 18:01:42.049287601 +0100
@@ -4981,7 +4981,7 @@ node *make_node(charinfo *ci, environmen
   case charinfo::TRANSLATE_DUMMY:
     return new dummy_node;
   case charinfo::TRANSLATE_HYPHEN_INDICATOR:
-    error("translation to \\% ignored in this context");
+    error("translation to \\%% ignored in this context");
     break;
   }
   charinfo *tem = ci->get_translation();