tests: use killdaemons in hgweb tests
hgweb tests often failed on my system because the serve port wasn't free when a
new hgweb was started; the killed hg wasn't completely dead yet.
Now we use killdaemons which waits for the process to die.
To run the tests, do:
cd tests/
python run-tests.py
See http://www.selenic.com/mercurial/wiki/index.cgi/WritingTests for
more information on writing tests.