mod_http_oauth2: Use numeric for loop instead of ipairs Pedantic attempted optimization, reducing function calls. I didn't even measure, only vaguely recall that this is faster in PUC Lua.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```