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More improvements to boolean tools. The main change (although very little in
code) is changing fuzzy comparisons of floating point values. For testing, a
new define is added in intern/boolop/intern/BOP_MathUtils.h called
VAR_EPSILON, which enables better comparisons. This is turned on by default;
undefining it will revert to using the previous comparisons. The downside of
these new comparisons is a loss in speed, but the resulting meshes are more
likely to be manifold (although still not always).
The other changes include speed improvements based on profiling results and
fixes for the improper creation of triangular faces with only two vertices.
178dc73084