Update all cc code using .clang-format; please do so as well for future PRs
etc.; emacs has a handy 'clang-format' mode to make this automatic.
For comparing old changes with git blame, we can disregard this one using
--ignore-rev
(see https://www.moxio.com/blog/43/ignoring-bulk-change-commits-with-git-blame )
Implement a new message indexer consisting of a single-threaded scanner
and a multi-threaded indexer.
This allows for a number of optimizations as well as background
indexing, though this initial version should be behave similar to the
old indexer.
