The version number has always been pretty meaningless to the user and
it's about to become even more meaningless with the introduction of
"features". Hopefully, the database will remain on version 3 for some
time to come; however, the introduction of new features over time in
version 3 will necessitate upgrades within version 3. It would be
confusing if we always tell the user they've been "upgraded to version
3". If the user wants to know what's new, they should read the news.
All we do here is calculate the backup filename, and call the existing
dump routine.
Also take the opportunity to add a message about being safe to
interrupt.
Test the upgrade from probabilistic to boolean folder: terms, and
addition of path: terms.
The test depends on the pre-built test corpus and database tarball and
checksum file being in place. If it's not, the test is skipped. The
mechanism to fetch the test database will be added later.
At the time of writing, a working test database and checksum file is
available at
http://notmuchmail.org/releases/test-databases/
It has been noted that some non-GNU environments make lack
sha256sum. We leave this portability issue for a followup patch.
