Localize the `authenticatior()` and `session_retrieve()` functions into the `index()` function scope so that they're retained when extracting the function into the dispatcher bytecode cache. Also allow access to the global scope since upvalues do not work reliably due to the out-of-context byte code caching of index functions. Fixes https://github.com/openwrt/luci/issues/1300#issuecomment-381352765 Fixes feefc600e ("luci-mod-rpc: rework authentication and session handling") Signed-off-by: Jo-Philipp Wich <jo@mein.io>