import: use ui.allowemptycommit to allow empty commits
Previously import used force=partial to allow empty commits to be made. Let's
switch it to using the new ui.allowemptycommit option. Tests says we can drop
the 'force' argument in the processs.
.. Common link and substitution definitions.
.. |hg(1)| replace:: **hg**\ (1)
.. _hg(1): hg.1.html
.. |hgrc(5)| replace:: **hgrc**\ (5)
.. _hgrc(5): hgrc.5.html
.. |hgignore(5)| replace:: **hgignore**\ (5)
.. _hgignore(5): hgignore.5.html