option defaults: defaults for inode-limit & aris

A small change, but it would be good to make it early on.
These changes should probably be mentioned in the release notes.

Set these as hardcoded defaults:

FileCacheInodeLimit 500000
AvoidRenamingIntrospectiveJavascript on

Fixes https://github.com/pagespeed/ngx_pagespeed/issues/284