adding a second notify to the fork and clone observers

[Andrew Cagney <cagney at redhat dot com>]

Sami, Phil,

While working on getting frysk to automatically detach from a new 
unobserved child process (created via fork) I had the chance to look 
again over the fork and clone observer methods.

At present they have a single notify method of the form:

 Action updateForked (Task parent, Task child);

that's called when the parent's fork event occurs.  If it blocks the 
parent, it also blocks the child as a side effect.  I'd like to suggest 
two changes:

- rename updateForked to updateForkedParent and have it only block the 
parent task
- adding a second method like:
 Action updateForkedChild (Task parent, Task child)
 called when the child is ready and it blocks just the child.

(I'm not sure if Sami and I discussed this before).
By having the two separate interfaces:
- blocking the child is separate and explicit (and can be done 
independent of the parent)
- there's clear and explicit point at which the child is in a state 
where it can be manipulated
Of course cascading code would need to be modified.  The new code would 
look like:

 updateForkedParent
   return CONTINUE

 updateForkedChild
   child.requestAddObserver...
   child.requestUnblock (this)
   return BLOCKED

thoughts?
Andrew