fixed access denied error messages

[skoef]

Not sure what went wrong trying to rebase #592 so here is a new attempt:

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When trying to reproduce my issue as I describe in #578 I came across an omission I made in #589: I directly pass the error code to NewDefaultError instead of the error message corresponding to that code. My apologies for the poor testing.

Also, I noticed that in a different case, the formatting of the user/address was the wrong way around in the access denied error. This gave

ERROR 1045 (28000): Access denied for user '127.0.0.1:51221'@'root' (using password: NO)

and now it correctly gives:

ERROR 1045 (28000): Access denied for user 'root'@'127.0.0.1:51259' (using password: NO)