Factor out strnstr() since posix hasn't got it, and add a config option for
the deeply sad passwd heuristics that don't even check numbers and punctuation.
diff --git a/lib/lib.c b/lib/lib.c
index 6559030..681d4d2 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -1033,3 +1033,14 @@
 
   return 0;
 }
+
+// Posix inexplicably hasn't got this, so find str in line.
+char *strnstr(char *line, char *str)
+{
+  long len = strlen(str);
+  char *s;
+
+  for (s = line; *s; s++) if (!strncasecmp(s, str, len)) break;
+
+  return *s ? s : 0;
+}