Blender Git Loki

Fix T38873: Crashing on undo of ocean modifier.

Issue of this bug is that most part of fftw is not thread safe, only compute-intensive fftw_execute & co are.

Since smoke was affected by this issue as well, a global fftw mutex was added to BLI_threads.
Audaspace also uses fftw in one of its readers (AUD_BandPassReader.cpp),
but this is not an issue currently since this code is disabled in CMake/scons files.

There was another threading issue with smoke, we need to copy dm used by emit_from_derivedmesh(),
as it is modified by this func.

Reviewers: sergey, brecht

Reviewed By: brecht

CC: brecht

Differential Revision: https://developer.blender.org/D374