Investigate legacy authentication with non-ASCII characters in passwords

[mrotteveel]

While looking at https://github.com/FirebirdSQL/NETProvider/issues/1217 (which was originally reported against this repository), I did reproduce problems with using special (non-ASCII) characters in passwords with legacy authentication.

That is odd as the OP reported that it did work with DBeaver (which uses Jaybird). In any case, this needs to be looked into further. One of the suspects is LegacyHash (6+) /UnixCrypt (5) as it works with char values, while I suspect it should be using bytes; but then the question is: in which character set?

Marking it against 7-initial for now; needs also to be verified against 5.0.x and 6.0.x.