Object extend is broken on SMP

[Sebastian Huber]

The object identifier to control mapping is done like this:

the_object = information->local_table[ index ]

The object extension allocates a new local_table and frees the old one. Thus the sequence above may access freed memory under certain cases.

Possible solutions:

1. Disable interrupts and make sure that the old table stays valid for a long enough time period after the registration of the new table. This timing depends on the particular hardware and may lead to very hard to find bugs.

2. Use a generation count, e.g. update the generation count during local table updates and make sure the generation count didn't change during local table reads.

[Sebastian Huber <sebastian.huber@…>]

In b80156cf15a9e080e8608a30e3e2795211c03f3e/rtems:

score: Avoid Giant _Objects_Extend_information()

Avoid Giant lock for _Objects_Extend_information().

Update #2280.
Update #2555.