REPL defers to sh when a symbol isn't found.

src/pebblisp.c

@@ -618,6 +618,12 @@ void repl(struct Environment* env)
             free(oldBuf);
         }
         Object o = parseEval(buf, env);
+        if (isError(o, DID_NOT_FIND_SYMBOL)) {
+            cleanObject(&o);
+            system(buf);
+            free(buf);
+            continue;
+        }
         free(buf);
 
         size_t length;