Fixed bug and optimize code in TRON::tron

Fixed bug and optimize code in TRON::tron

Variable "iter" and "w" won't change in the
while loop of function TRON::tron when the
direction does not lead to sufficient
function-value decrease, so using expression
"iter == 1" as a flag to initialize variables
will cause problems in the first step.
We introduce a new variable "delta_adjusted" to
fix the bug.

The function call "fun_obj->get_diagH(M)" and the
calculation of "(1-alpha_pcg) I + alpha_pcg M"
can be saved if "iter" and "w" remains the same.
We move some lines of code to save the
calculation.