post_process prints to stdout on error

[MarekPikula]

I use frappe-client in my application and when the response is not JSON (eg. authentication didn't succeed) the library prints the response (website HTML) to the console. My app is a console-based, so this behaviour is highly undesirable, as the library fills the console with content of no significance to the user. I needed to suppress stdout, by using the approach shown here. I'd propose to at least add a flag, which suppresses printing by default and redirect the response handling to the main application in a meaningful way, for example by raising an exception on 401 error.

I'll be working on patch for this, but any feedback would be highly appreciated.

[MarekPikula]

I can see that there is AuthError implemented, but not used for token-based authentication. I'll use it for this.