exchange: use command executor for getbundle
The code consuming the bundle has been moved to inside the
context manager, as that is supposed to be part of the API.
(Although it doesn't matter for version 1 peers.)
Differential Revision: https://phab.mercurial-scm.org/D3316
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.