Bug#981731: Multi-threaded bullet

[Dima Kogan]

Hi. I'm updating the Debian package to the latest upstream version now.
And I can do the multi-threaded builds.

We have the following options:

  BULLET2_MULTITHREADING:

    Build Bullet 2 libraries with mutex locking around certain
    operations (required for multi-threading)

  BULLET2_USE_OPEN_MP_MULTITHREADING:

    Build Bullet 2 with support for multi-threading with OpenMP
    (requires a compiler with OpenMP support)

  BULLET2_USE_TBB_MULTITHREADING:

    Build Bullet 2 with support for multi-threading with Intel Threading
    Building Blocks (requires the TBB library to be already installed)

Which of these do we want? All of them?

Also, is there a good reason to build both multi- and single- threaded
versions? I propose to just build the multi-threaded libraries, and call
it good.