branchcache: add debug output whenever cache files use truncate
The cache files are usually append only but will automatically be truncated and
recover in exceptional situations. Add a debug notice when such exceptional
situations are encountered.
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.