Allow mysql spatial indexes

Allows spatial indexes via the SPATIAL flag.
http://dev.mysql.com/doc/refman/5.7/en/creating-spatial-indexes.html
Something I've just stumbled upon as I'm looking for SPATIAL indexes in Doctrine: http://mysqlserverteam.com/innodb-spatial-indexes-in-5-7-4-lab-release/
5.7.4 LAB release says that it supports Spatial indexes