1. Android.getScreenBrightness() is used in frontend/device/android/powerd.lua to retrieve the frontlight intensity.
2. kosync.koplugin won't save settings for whisper sync.
3. batterstat.koplugin won't work correctly if several on* events are fired.
MenuSorter: forgot to add plugin style change
MenuSorter: worked out the final quirks
* Menu always compressed into tables without missing indexes for ipairs compatibility
* Orphans attached
* Separators no longer count as items
1. It turns out that `device_id` is not defined in unit test environment
which makes the `assert(self.kosync_device_id)` fail and somehow makes `luajit` segmentation fault.
2. In the device spec, stubbing `io.open` will make subsquent `require`
all return boolean value and segmentation fault `luajit`.
This patch is a minimum viable change that makes CI work on both my
local box and Travis.
The 'KOSync' plugin will synchronize furthest reading progress
across different koreader devices after users registering their
devices.
The synchronizing service is open-sourced as the project
[koreader/koreader-sync-server](https://github.com/koreader/koreader-sync-server).
