[Bf-codereview] Bullet Integration (issue 7092051)

[ideasman42 at gmail.com]

Some things I should have mentioned last review...

- The way groups is used I find a bit strange, instead it could flag
objects and store in an array? - it works as is and may be annoying to
change right now but noting here.
Maybe other devs can explain why doing it this way is good.

- Think it would be good to have a check on the scene if physics should
run something like;
'bool BKE_scene_rigidbody_check(Scene *scene)',
The check only needs to see if the scene has a physics pointer and its
un-muted.
Then any place physics is done through the code this check can be
called.
Currently each function has to check in its body which I find less easy
to follow.

https://codereview.appspot.com/7092051/