fix trivial warnings

mainly unused parameter and unused function
some parameters are indeed used in a debug built, I used the
(void)(param) trick
warnings reported by clang 4

code/IFCCurve.cpp

@@ -564,6 +564,7 @@ IfcFloat Curve :: GetParametricRangeDelta() const
 // ------------------------------------------------------------------------------------------------
 size_t Curve :: EstimateSampleCount(IfcFloat a, IfcFloat b) const
 {
+    (void)(a); (void)(b);
     ai_assert(InRange(a) && InRange(b));
 
     // arbitrary default value, deriving classes should supply better suited values