[Bf-taskforce25] unique integer ids for ID types

[joe]

I had an idea the other day.  What if we store a unique integer id
(uid) in ID blocks, bones, nodes, etc?  This would solve a number of
issues, as I see it:

1. RNA paths would be faster and more reliable to resolve.  If you
rename an object, or a bone, or a material, the uid stays the same, so
there's no need to go through and update existing RNA paths.  And
looking up integer uids would be much faster then looking up names.
2. Things without names (e.g. nodes) require something like this,
since basing the RNA paths off of simple indices would be far too
unstable.
3. This might work for constraint targets, too; e.g. the constraint
would store a uid, but present the user with the same UI of typing in
a bone's name, of course.  This idea would probably need more thinking
through, however.

Joe