Merge branch 'jk/diff-algo-finishing-touches' into maint

"git diff --diff-algorithm=algo" was understood by the command line
parser, but "git diff --diff-algorithm algo" was not.

* jk/diff-algo-finishing-touches:
diff: allow unstuck arguments with --diff-algorithm
git-merge(1): document diff-algorithm option to merge-recursive

diff --cc diff.c
Simple merge