convert: add a mode where mercurial_sink skips empty revisions. The getchanges function of some converter_source classes can return some false positives. I.e. they sometimes claim that a file "foo" was changed in some revision, even though its contents are still the same. convert_svn is particularly bad, but I think this can also happen with convert_cvs and, at least in theory, with mercurial_source. For regular conversions this is not really a problem - as long as getfile returns the right contents, we'll get a converted revision with the right contents. But when we use --filemap, this could lead to superfluous revisions being converted. Instead of fixing every converter_source, I decided to change mercurial_sink to work around this problem. When --filemap is used, we're interested only in revisions that touch some specific files. If a revision doesn't change any of these files, then we're not interested in it (at least for revisions with a single parent; merges are special). For mercurial_sink, we abuse this property and rollback a commit if the manifest text hasn't changed. This avoids duplicating the logic from localrepo.filecommit to detect unchanged files.

#!/bin/sh

hg clone http://localhost:20059/ copy
echo $?
test -d copy || echo copy: No such file or directory

cat > dumb.py <<EOF
import BaseHTTPServer, SimpleHTTPServer, signal

def run(server_class=BaseHTTPServer.HTTPServer,
        handler_class=SimpleHTTPServer.SimpleHTTPRequestHandler):
    server_address = ('localhost', 20059)
    httpd = server_class(server_address, handler_class)
    httpd.serve_forever()

signal.signal(signal.SIGTERM, lambda x: sys.exit(0))
run()
EOF

python dumb.py 2>/dev/null &
echo $! >> $DAEMON_PIDS

# give the server some time to start running
sleep 1

http_proxy= hg clone http://localhost:20059/foo copy2 2>&1 | \
    sed -e 's/404.*/404/' -e 's/Date:.*/Date:/'
echo $?

kill $!