getopt: break after parsing opt
setopt: remove setting maxchild per process

Accidentally the maxchild option. maxchild is used to size an array of
file descriptors. So obviously resetting this value will either crash
the process (read outside the bounds of the array) or cause it leak fd's.

So punt for now and remove support for changing maxchild. I guess the
simplest way to handle this would be to:

* get the new value of maxchild
* allocate an array of maxchild bytes
* copy PIDs from old to new
* if there is not enough space, free new array and return badarg
* otherwise, point the state to the new array and free the old array

Instead of crashing the caller by returning badarg, we could synthesize
an errno value and return {error,enomem} or simply leave the maxchild
unchanged and return ok.