Merge branch 'mk/show-s-no-extra-blank-line-for-merges' into maint

"git show -s" (i.e. show log message only) used to incorrectly emit an extra blank line after a merge commit. * mk/show-s-no-extra-blank-line-for-merges: git-show: fix 'git show -s' to not add extra terminator after merge commit