1) Is breakpoint validated on "language layer"? So, can breakpoint be
validated indempendently on concrete debugger plug-in (= debugger
implementation).
2) Is breakpoint validated on "debugger plug-in layer"? Can breakpoint
be validated by debugger plug-in even if no debugger session is
started for this debugger plug-in?
In this case engine should "ask" all registered debugger plug-ins for
concrete "breakpoint request".
or
3) Should be breakpoint validated for concrete debugger session only?
It means you need some connection to running debugger engine to
validate request for breakpoint.
In this case I do not know what to do if there is no running session.
That is why I need to see some UI specs. for your debuggers.

We should support 2 + 3, I think.

Solution should support this scenario (Ivan S.):

We make a rule that says the _engine_ maintains the ultimate state.
This engine can be an external engine interacting with the gui through 
a proxy/surrogate or it could be more tightly tied like jpda is. The 
bpt interaction will then looks like this:

Positive Scenario
	- user clicks on the glyph gutter.
	- gui _doesn't_ create a Bpt object
	- gui sends "new bpt" message to external engine
	- external engine creates Bpt object.
	- external engine tells gui that it created a Bpt object
	- gui creates Bpt object.
Thsi will work cleanly if the bpt creation is initiated in the engine.

the gui will not have to futz with deciding whether the initiation was
from the gui or independently from the engine.	
	
Negative scenario	
	- user clicks on the glyph gutter.
	- gui _doesn't_ create a Bpt object
	- gui sends "new bpt" message to external engine
	- external engine decides bpt is invalid.
	- external engine sends the gui a generic error message
	- gui _doesn't have to clean a Bpt object of its own.

# validation of breakpoints:

   1. when brakpoint is created - there should be possibility to
refuse the breakpoint - that it will not be created
   2. and later we have some glyph mapped on breakpoint.valid
property. Ouestions:  what does it mean valid breakpoint?, once vaild
= valid forever???

Fixed.
1) valid property has been moved out from debugger API
2) toggling of breakpoints is responsibility of debugger plug-ins now,
see BreakpointsProvider.toggleBreakpoint ()

Verified ... and Closing all issues resolved into NetBeans 6.7 and earlier.