Connection error with sslmode (PgSQL 7.3)

Hello,

I register problem with connection to PgSQL 7.3. Error is that
PgSQL 7.3 doesn't know connection parameter sslmode.

I think about it and try this solution:
Add SSL mode:
- none - don't add sslmode to connect string
- requiressl_try - use requiressl=0 instead of sslmode
- requiressl_on - use requiressl=1 instead of sslmode

I also change default value from "prefer" to "none". "none" works
aginist all server versions.

There is a question what about Protocol data source option? Isn't
it obsolete?

Comments all welcome

Luf