forbid username with '\n' at the changelog level
It was already forbidden for ui.username() but no verification were
made for username passed through the commandline.
adding a
transaction abort!
rollback completed
abort: username 'foo\nbar1' contains a newline
transaction abort!
rollback completed
abort: username 'foo\nbar2' contains a newline
transaction abort!
rollback completed
abort: username 'foo\nbar3' contains a newline!