Backported ODBC driver for PostgreSQL

New functions can used to escape BLOBs:

```erlang
Format = ejabberd_odbc:escape_format(Host),
ejabberd_odbc:escape_binary(Format, Bin).
```

While MySQL uses the same escaping format both for binaries and strings, Postgres escapes binaries with [bytea hex format](http://www.postgresql.org/docs/9.0/static/datatype-binary.html).
This PR was tested with PostgreSQL 9.0.