Cost function and gradient passes the test
Change of notation '_T' -> '_Adj' (clarity)

'_TL' still stant for 'tangent linear'.  But from
now on, the adjoint of an operator will be noted
by appending '_Adj'.
kdVar in alpha phase!

Assimilation is working, but there subsist a -1
factor I have to put in gradCostFunc for which
I have no explanation yet.  Removing it make the
gradient test negative (~ -1.) and the
minimization fails.