PDO odbc patch

Morning,

I found an issue this week that exists in both odbc and pdo_odbc with
SQL Server. The ODBC implemention of Windows returns 0 as the length
for for varchar(max) nad nvarchar(max). This makes the allocation of
the strings incorrect and you get back garbage pointers for the
contents.

This was a pretty easy fix for pdo_odbc, simply check if the colsize
is returned as 0 and the type is one of the varchar types, if so
always treat it as a column with "long" data. This works perfectly
without breaking things. Attached is a patch that works for both 5.3
and trunk, includes an additional test for the issue.

The odbc extension is turning out to be more of a pain, each function
is doing it's own fetching so it either has to be fixed for each
function, or change odbc to use a single function for all fetching,
which might break bc.

Thanks,
Elizabeth M Smith