RFE#919: Multiple-column foreign key relation.

RFE#919: Multiple-column foreign key relation.
https://sourceforge.net/p/phpmyadmin/feature-requests/919/

![rfe_919_2](https://cloud.githubusercontent.com/assets/6863616/3768239/4ed96b8e-18d5-11e4-89c2-8a7cd3ca43f5.png)

Signed-off-by: Ashutosh Dhundhara <ashutoshdhundhara@yahoo.com>