Make absolutely sure that tau is initialized (this change suppresses a gcc warning)

--HG--
branch : 3.2
Free functions should only be declared as static in separate compilation units

--HG--
branch : 3.2
Removed unused typedef

--HG--
branch : 3.2
BVH appears to compile well with clang (re-enabled unit test)

--HG--
branch : 3.2