doc/common.txt

keyword: do not bother about detecting extension path in demo

Detecting and showing the path to a keyword extension in a
non-standard place only made sense while keyword.py was not
shipped with Mercurial.

The test output has changed because we do not have a spurious
space at eol anymore.

.. 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