revset: special case commonancestors(none()) to be empty set
This matches the behavior of ancestor(none()).
From an implementation perspective, ancestor() and commonancestors() are
intersection, and ancestors() is union, so it would make some sense that
commonancestors(none()) returned all revisions. However, ancestor(none())
isn't implemented as such, which breaks ancestor(x) == max(commonancestors(x)).
From a user perspective, ancestors of nothing is nothing whichever type
of operation the ancestor predicate does.
# Apache won't be able to resolve its own hostname, so we sneak this
# into the global context to silence a confusing-to-user warning on
# server start.
ServerName hg
<VirtualHost *:80>
DocumentRoot /var/hg/htdocs
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
SetEnv HGENCODING UTF-8
SetEnv LC_TYPE UTF-8
WSGIDaemonProcess hg processes=${WSGI_PROCESSES} threads=${WSGI_THREADS} maximum-requests=${WSGI_MAX_REQUESTS} user=www-data group=www-data display-name=hg-wsgi
WSGIProcessGroup hg
WSGIScriptAliasMatch ^(.*) /var/hg/htdocs/hgweb.wsgi$1
ErrorLog ${APACHE_LOG_DIR}/error.log
LogLevel warn
CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>