help: better explanation for some of the environment variables
In particular, the precedence for usernames is explained in more detail.
Thanks to timeless for pointing out the deficiencies here.
adding a
abort: username 'foo\nbar1' contains a newline
abort: username 'foo\nbar2' contains a newline
transaction abort!
rollback completed
abort: username 'foo\nbar3' contains a newline!