[phobos] Returning Scoped Allocators From Functions

[David Simcha]

I'm working on retrofitting TempAlloc (renamed to RegionAllocator)to fit 
Andrei's proposed allocator interface.  One issue I've run into is, what 
happens when a scoped allocator is returned from a function?  For example:

RegionAllocator fun() {
     RegionAllocator alloc;
     alloc.malloc(42);

     RegionAllocator alloc2;
     alloc2.malloc(42);
     return alloc2;
}

Now, alloc has died and alloc2 is still alive, violating LIFO 
requirements.  Since it's virtually impossible to do by mistake, I'm 
inclined to just make returning a RegionAllocator from a function after 
another one has been subsequently created undefined behavior.

Also, while we're on the subject, does anyone have any serious 
objections to me keeping frameInit/regionInit and frameFree/regionFree 
(they've been renamed) public but undocumented?  I need to write a 
wrapper around this new interface to simulate the old interface and 
avoid breaking a whole bunch of old code I've written.  I don't see any 
way to do this without these functions exposed.  Furthermore, they might 
be useful to people looking to build their own policies on top of 
RegionAllocator's low-level mechanisms.  Generally I believe that stable 
low-level features should be exposed to avoid ugly abstraction inversions.