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.
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
removing b
created new head
% should abort
abort: crosses branches (use 'hg merge' or 'hg update -C' to discard changes)
% should succeed
abort: crosses branches (use 'hg merge' or 'hg update -C')