mpatch: use absolute_import
While I was here, I removed the try..except around importing cStringIO
because cStringIO should always be importable on modern Python versions.
We already do an unconditional import in other files.
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.