Re: Extending a bit string

That's SQL:99 6.22 <cast specification> general rule 11) c).
(SV and TD are the source value and the target datatype for a cast.)

In hindsight, it would likely be more consistent with this if we'd
considered bitstrings to be LSB first when coercing them to/from integer,
but whoever stuck that behavior in didn't think about it.  Too late to
change that now I'm afraid, though perhaps we could provide non-cast
conversion functions that act that way.