Merge branch 'rk/commit-tree-make-F-verbatim' into maint

Unlike "git commit-tree < file", "git commit-tree -F file" did not
pass the contents of the file verbatim and instead completed an
incomplete line at the end, if exists.  The latter has been updated
to match the behaviour of the former.

* rk/commit-tree-make-F-verbatim:
  commit-tree: do not complete line in -F input