demandimport: remove support for Python < 2.5
The removed code was to support an __import__ function that doesn't
support the "level" argument. This argument was added in Python 2.5,
which we no longer support.
Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:
http://docutils.sourceforge.net/rst.html
It's also convertible to a variety of other formats including standard
UNIX man page format and HTML. You'll need to install Docutils:
http://docutils.sourceforge.net/
Use the Makefile in this directory to generate the man and HTML pages.