Robert Maynard tells me that the TBB backend has been tried on versions
of TBB back to 4.0. Since the patch appears to work across them, allow
those versions too.
We have a patched version of TBB's parallel_for.h in our files that
fixes a problem with using std::swap. This issue has since been fixed in
TBB, so for newer versions we should revert back to TBB's
implementation.
On one of my compile platforms, GCC was giving conversion warnings from
any boost include that was not wrapped in pragmas to disable conversion
warnings. To make things easier and more robust, I created a pair of
macros, VTKM_BOOST_PRE_INCLUDE and VTKM_BOOST_POST_INCLUDE, that should
be wrapped around any #include of a boost header file.
tbb includes windows.h, and doesn't use the NOMINMAX so we need to do
that ourselves so that we can use std::min/max and limits<T>::min/max.
At the same we also define WIN32_LEAN_AND_MEAN so that the total number of
macros that windows.h defines is reduced.
The previous implementation assumed the identity value to be zero, which does
not work for multiplication. Changed the interface to require an initial value
for Exclusive Scan with custom operator (TBB Device only, for now).
