Remove FLAG_INTERACTIVE test from "login as:" prompt. Kelly John Carney

Remove FLAG_INTERACTIVE test from "login as:" prompt. Kelly John Carney
pointed out that Plink would attempt to use a zero-length username iff
a remote command was specified (because the FLAG_INTERACTIVE test was
erroneously combined with the no-username test).

I don't think this will break non-interactive use; in the cases which
behave differently, Plink would be attempting to use the empty
username, which was almost certainly wrong, whereas now it will give a
prompt (which can be avoided with -batch as usual).

(Although perhaps we should attempt to use a local username as a guess for
the remote username, as PSCP does? I've not done this.)

git-svn-id: svn://svn.tartarus.org/sgt/putty@4831 cda61777-01e9-0310-a592-d414129be87e