Bugfix in approve operations - signer must be 'who', not 'from'

[ray66rus]

In some cases (EscrowApprove, EscrowDispute, EscrowRelease) operations the person who wants to do this operation can be different from the person, who is stated in the "from" field. In EscrowApprove, for example, it can be "to" or "agent". So this operation must be signed not by "from", but by "who".

[marvin-we]

Here is the original Steem code:

void get_required_active_authorities( flat_set<account_name_type>& a )const{ a.insert(who); }

So yes, you are totally right! :) Thanks for that!