use of OID.Unknown

Before we cut an 8.1 stable release, I'd like to revisit the use of
unknown for strings at a minimum.

Currently the driver exhibits some non-intuitive behaviour.

1) Not using indexes unless the correct type is bound to the
parameter ( this is intuitive as I write it but many users get
tripped up ). I'm not sure using unknown for strings would help here
but the other option is using unknown for everything and let the
backend decide what type to use. This may be an option if we only do
this when prepareThreshold is 0 since we assume that we won't be
caching plans anyway.

2) We have broken backward compatibility by changing the behaviour of
setString.

At a minimum I'd propose we bind strings to unknown.

For or against ?

Dave