Flush while searching in included files

This fixes a problem where the completion menu would not pop up
immediately when hitting Ctrl-n to complete an identifier in a .pl file.

src/search.c

@@ -5154,6 +5154,12 @@ find_pattern_in_path(ptr, dir, len, whole, skip_comments,
 		goto search_line;
 	}
 	line_breakcheck();
+#ifdef FEAT_GUI_MACVIM
+	/* This loop could potentially take a long time, so make sure MacVim
+	 * gets a chance to flush its output. */
+	if (gui.in_use)
+	    gui_macvim_flush();
+#endif
 #ifdef FEAT_INS_EXPAND
 	if (action == ACTION_EXPAND)
 	    ins_compl_check_keys(30);