Start the merging-rebase to upstream/maint

This commit starts the rebase of b213911 to 49800c9

This merging rebase was started not because upstream's `maint` branch
advanced (it did not), but to replace a couple of patches with newer
iterations, as sent to the upstream Git project independently. In
particular, those are:

- The patch series merged by fe73baf
  (jeffhostetler/jeffhostetler/quick_add_index_entry) was replaced by
  the most recent iteration of 'jh/add-index-entry-optim' (b986df5)

- The Pull Request jeffhostetler/jeffhostetler/string_list_realloc
  merged via c775bdd was replaced by the latest iteration of
  'jh/string-list-micro-optim' (950a234)

- The jh/memihash-opt patches merged by 2862058 were replaced by the
  newest iteration (41b3eb4)

- The bug fix where difftool used a buffer after freeing it
  (d33e487) was replaced by the one that made it into upstream
  (882add1)

- The patch in the `coverity` series that tried to fix a resource leak
  in git-am (a520816) was replaced by a better patch submitted by
  Ren_ Scharfe (ac8ce18)

- The patch in the `coverity` series that tried to fix a resource leak
  in the `handle_ssh_variant()` function (f07be76) has been dropped,
  as a different patch had been accepted into `pu` already

- The rebase-i-extra patches (e1be548) were replaced by the latest
  iteration (1d3d10b)

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho