osx fix
add Multiblock example.  Vortex / Jacobian calculation with user-specified unit.
Multiblock:
	modified:   VTK/MultiBlockVectorFieldVTK.cxx
	new file:   VTK/examples/StreamlineRenderMultiBlock.cpp
Vortex / Jacobian computation:
	modified:   src/Field.C
	modified:   src/Field.h
Merge remote-tracking branch 'origin/osx_fix'

Conflicts:
	VTK/MultiBlockVectorFieldVTK.cxx
minor changes