[Box] variable switch at boundary

It seems that there is a bug in the variable switch for box at the boundary. In the initPriVarSwitch_ method, the states of Dirichlet nodes are corrected. This method is called in newtonBegin, which however is called after the initialization of uLastIter.

Therefore, when calling the newtonUpdate method, the corrected states of uCurrentIter are overwritten.

We could fix this by either calling initPriVarSwitch_ before uLastIter is initialized or by setting this vector after newtonBeginStep. So we could simply change

if (numSteps_ > 0)
    uLastIter = uCurrentIter;

to

if (numSteps_ >= 0)
    uLastIter = uCurrentIter;