Check command name/path for truncation and provide user feedback during

config parse (and use conf_cmd_add to populate defaults); based on a
discussion with Tiago Cunha.  While this looks ugly, there are likely
some other changes here to come.

parse.y

@@ -137,7 +137,12 @@ main		: FONTNAME STRING		{
 			conf->snapdist = $2;
 		}
 		| COMMAND STRING string		{
-			conf_cmd_add(conf, $2, $3);
+			if (!conf_cmd_add(conf, $2, $3)) {
+				yyerror("command name/path too long");
+				free($2);
+				free($3);
+				YYERROR;
+			}
 			free($2);
 			free($3);
 		}