BUG/MEDIUM: checks: Make sure the tasklet won't run if the connection is closed.

BUG/MEDIUM: checks: Make sure the tasklet won't run if the connection is closed.

wake_srv_chk() can be called from conn_fd_handler(), and may decide to
destroy the conn_stream and the connection, by calling cs_close(). If that
happens, we have to make sure the tasklet isn't scheduled to run, or it will
probably crash trying to access the connection or the conn_stream.
This fixes a crash that can be seen when using tcp checks.

This should be backported to 1.9 and 2.0.
For 1.9, the call should be instead :
task_remove_from_tasklet_list((struct task *)check->wait_list.task);
That function was renamed in 2.0.