Comment 5 for bug 1466021

I assume some sort of 'best effort' is worth it here. So, when system settings opens, see if the / filesystem is mounted writeable.

If so, set a flag, and remember it forever (well, until the handset is factory reset, or flashed with u-d-f --bootstrap)

This won't catch all cases, but it will catch many.

Additionally, the phablet-tools scripts which are the 'official' means of marking writeable could collaborate and also set this flag.

Note that if a user can reset this flag by hand in the terminal, that's fine. The intention is to assist communication with users who don't fully understand the consequences/