Add Connector/ODBC to default odbcinst.ini on Mac

The installer for Connector/ODBC should add the information about the connector to ODBCINST.INI in the default location on Mac, which is /Library/ODBC/odbcinst.ini. In case the directory and/or file does not exist it should be created. If the file exists new information should be appended to it, since there likely is other connectors/drivers defined in it already.

This should be added to a post installation script of the pkg installer.