nothing. Stops the t and sets its state to 'stopped'.
Note:
A task whose state is not 'started' cannot be stopped.
Intermediate results are discarded when a task is stopped.
killTask() should be called for any no longer needed task.
Example:
LIB "tasks.lib";
ring R = 0, (x,y), dp;
ideal I = x9y2+x10, x2y7-y8;
task t = "std", list(I);
startTasks(t);
stopTask(t);
t;
==> A task with the following properties:
==> command: std
==> no. of arguments: 1
==> state: stopped
==>
killTask(t);