Blender Git Loki

Cleanups:

- rework includes order in intern/openvdb: first include should be the
source file's header, then other header in the same directory, following
by system/library headers and finally other local headers.

- move ScopeTimer cdtor definitions to openvdb_util.cc, no reason for
them to be in a header.

- add a DEBUG_TIME macro to switch Timer macro on and off instead of
using NDEBUG macro (doesn't make much sense to time in debug mode)