[PATCH 07 of 10] chgserver: implement validate command

[Jun Wu]

On 03/03/2016 04:06 PM, Yuya Nishihara wrote:
> It seems awkward that the input has no last '\0', but the output has, though
> I know validate() have to return something even if insts is empty.

The input is consistent with runcommand and getpager. Since there are 3
commands using a same input, I have considered adding another command for just
passing "args" beforehand. But maintaining compatibility for runcommand is hard
so I gave up.