This was completely wrong: it overflowed on large filesystems and
double-counted the used bytes.
The new logic is still imperfect in that if there are a bunch of files in the
process of being deleted (moved from recording to reserved_sample_files but
not yet unlinked), they'll be taken out of the total capacity. Maybe it should
stat everything in the sample file directory instead of relying on the
recording table. It's definitely an improvement, though.
This page was noticeably slower than necessary because the recording_cover
index wasn't actually covering the query. Both the schema for new databases
and the upgrade query were broken (and not even in the same way).
No new schema version to correct this, at least for now. I'll probably have
another reason to change the schema soon anyway and can throw this in.
This makes it easier to understand which options are valid with each
command.
Additionally, there's more separation of implementations. The most
obvious consequence is that "moonfire-nvr ts ..." no longer uselessly
locks/opens a database.
