COMP: Conditional assert check warning unused var.

ITKv4/Modules/ThirdParty/VNL/src/vxl/core/vnl/vnl_diag_matrix.h:82:47: warning:
      unused parameter 'j' [-Wunused-parameter]
inline T& operator () (unsigned i, unsigned j) {

Change-Id: I8ca952cdbea58ab42879bfe362ed7a1ef505db1c
Merge branch 'fix-vnl-diag-matrix-warning'

This is a patch submitted from the ITK community

* fix-vnl-diag-matrix-warning:
  COMP: Conditional assert check warning unused var.