Removed dead code special-casing isnan()

Change-Id: I27301b51d282215e850fa28f0769823c27c318be
Removed unused VTK_SIGN macro

Change-Id: I52e5a6b213cf1e3a9cfa19759e7f54028eb5b0db
Use vtkMath::IsNan unconditionally instead of isnan()

Change-Id: Ic09b8c96fcfbbf4ce38b1d9eed6253714ba668ec
vtkMath::IsNan is now inline making the special-casing uncessary
Removed special case for gcc 3 on OS X

VTK requires 10.5+ now, where gcc 4.0 and 4.2 are available.
No dashboard tests this path anyway.

Change-Id: If7ce8a916ff97376c3e4689c88ad998469a8ac16
Merge topic 'vtkmath-cleanup' into master

35985004 Removed special case for gcc 3 on OS X
5357c3d5 Use vtkMath::IsNan unconditionally instead of isnan()
7fe84db3 Removed unused VTK_SIGN macro
40e037fa Removed dead code special-casing isnan()