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.
% directory moved and symlinked
adding foo/a
% now addremove should remove old files
adding bar/a
adding foo
removing foo/a