sdist: Accept -u/--owner and -g/--group options

Controlling the file ownership recorded in tar archives is useful for
those striving towards reproducible builds. These options are already
understood by distutils.command.sdist.sdist, so just need to be accepted
by setuptools.command.sdist.sdist to be propagated.

Fixes #1893.

changelog.d/2800.change.rst

@@ -0,0 +1,3 @@
+Added ``--owner`` and ``--group`` options to the ``sdist`` command,
+for specifying file ownership within the produced tarball (similarly
+to the corresponding distutils ``sdist`` options).

setuptools/command/sdist.py

@@ -31,6 +31,10 @@ class sdist(sdist_add_defaults, orig.sdist):
         ('dist-dir=', 'd',
          "directory to put the source distribution archive(s) in "
          "[default: dist]"),
+        ('owner=', 'u',
+         "Owner name used when creating a tar file [default: current user]"),
+        ('group=', 'g',
+         "Group name used when creating a tar file [default: current group]"),
     ]
 
     negative_opt = {}