Added callback routines for PostgreSQL >= 9.2

Hello Zheng,

as odbc_fdw is linked from the Postgres WIKI, I found is kind of bitter that it did not compile with a recent version.

Thus I've added the required new callbacks for PostgreSQL >= 9.2 (still read-only) based on tds_fdw (https://github.com/GeoffMontee/tds_fdw).

I'm anything but a C hacker, but I'm pretty sure I've done the basics right. And it compiles ;-)
However, this is completely untested (I will hopefully be able to test it in the next days with a M$-SQL-DB though).

Best regards,

Gunnar "Nick" Bluth