Prioritize grab_as over hash with username:hash

[cardonator]

Hi, for endpoints like createThread it would be really nice if grab_as was prioritized if it was passed. The scenario is I'm logged in as joe with hash 1234567890 and my application is written to allow joe to post as bob (user id 111).

In this scenario I pass something like: action=createThread&node_id=580&hash=joe:1234567890&title=Testing+XenApi&message=This+should+be+the+%5Bb%5DPOST+CONTENT%5B%2Fb%5D+BY+bob&grab_as=111

However the post still comes from joe.