The original nmbug format (now called version 0) creates 1
subdirectory of 'tags/' per message. This causes problems for more
than (roughly) 100k messages.
Version 1 introduces 2 layers of hashed directories. This scheme was
chose to balance the number of subdirectories with the number of extra
directories (and git objects) created via hashing.
This should be upward compatible in the sense that old repositories
will continue to work with the updated notmuch-git.
Commits or checkouts that modify a large fraction of the messages in
the database should be relatively rare (and in some automated process,
probably non-existent). For initial setup, where such operations are
expected, the user can pass --force.
This is probably more convenient than always passing a command line
argument.
Use notmuch-config for consistency with other notmuch CLI tools.
Now that there is something relevant in the config files, test the
--config option.
The previous defaults were not suitable for personal (i.e. not
bugtracking for notmuch development) use.
Provide two ways for the user to select nmbug compatible defaults;
command line argument and checking the name of the script.
