support non-success return codes

[Thomas Waldmann]

on bepasty, we may require login for being able to create pastebins.

while playing with pastebinit, I often failed to submit until i got the login working - bepasty returns a 403 status in such cases.

but pastebinit gives no direct indication that submission did not work.

in our case i only could say it was not working as it gave me the upload url and not the usual unique-url for the new pastebin.

not sure what the best way is to tell about unsuccessful submission (considering pastebinit could be used by other tools and not just humans). maybe just do not output any url at all if unsuccessful? even that would be better than outputting a url that is not the desired pastebin.